{"id":"CVE-2026-27205","aliases":["CLSA-2026-1789727592","CLSA-2026-1789986000","CLSA-2026-1789986625","CLSA-2026-1789986626","CLSA-2026-1789987201","DEBIAN-CVE-2026-27205","EUVD-2026-7731","GHSA-68rp-wp8r-4726","OESA-2026-2135","OESA-2026-2136","OESA-2026-2137","PYSEC-2026-2151","ROOT-APP-PYPI-CVE-2026-27205","SUSE-SU-2026:0849-1","SUSE-SU-2026:22023-1","UBUNTU-CVE-2026-27205","USN-8104-1","openSUSE-SU-2026:10264-1","openSUSE-SU-2026:20885-1"],"status":"published","title":"Flask session does not add `Vary: Cookie` header when accessed in some ways","description":"Flask is a web server gateway interface (WSGI) web application framework. In versions 3.1.2 and below, when the session object is accessed, Flask should set the Vary: Cookie header., resulting in a Use of Cache Containing Sensitive Information vulnerability. The logic instructs caches not to cache the response, as it may contain information specific to a logged in user. This is handled in most cases, but some forms of access such as the Python in operator were overlooked. The severity and risk depend on the application being hosted behind a caching proxy that doesn't ignore responses with cookies, not setting a Cache-Control header to mark pages as private or non-cacheable, and accessing the session in a way that only touches keys without reading values or mutating the session. The issue has been fixed in version 3.1.3.","severity":{"version":"4.0","score":2.3,"vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N","level":"low","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-09","score":0.004,"percentile":0.3457,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-524"],"published":"2026-02-19T20:45:41Z","modified":"2026-10-28T02:30:22Z","fixes":[{"ecosystem":"PyPI","package":"flask","fixed_in":["3.1.3"],"sources":["ghsa","osv"]},{"ecosystem":"TuxCare:PyPI","package":"flask","fixed_in":["2.2.5.post1+tuxcare","1.1.4.post3+tuxcare","1.1.2.post2+tuxcare"],"sources":["osv"]},{"ecosystem":"Debian:13","package":"flask","fixed_in":["3.1.1-1+deb13u1"],"sources":["osv"]},{"ecosystem":"Debian:14","package":"flask","fixed_in":["3.1.3-1"],"sources":["osv"]},{"ecosystem":"openEuler:24.03-LTS-SP3","package":"python-flask","fixed_in":["2.2.5-2.oe2403sp3"],"sources":["osv"]},{"ecosystem":"openEuler:24.03-LTS","package":"python-flask","fixed_in":["2.2.5-2.oe2403"],"sources":["osv"]},{"ecosystem":"openEuler:24.03-LTS-SP1","package":"python-flask","fixed_in":["2.2.5-2.oe2403sp1"],"sources":["osv"]},{"ecosystem":"Root:PyPI","package":"rootio-Flask","fixed_in":["3.1.2+root.io.1","3.1.2+root.io.2","3.1.1+root.io.1","3.1.1+root.io.2","3.1.2+root.io.3","2.3.3+root.io.1","2.3.3+root.io.2","3.0.3+root.io.1"],"sources":["osv"]},{"ecosystem":"Root:PyPI","package":"Flask","fixed_in":["3.1.1+aikido.2","3.1.2+aikido.3"],"sources":["osv"]},{"ecosystem":"SUSE:Linux Enterprise Module for Python 3 15 SP7","package":"python-Flask","fixed_in":["2.3.2-150400.3.9.1"],"sources":["osv"]},{"ecosystem":"openSUSE:Leap 15.6","package":"python-Flask","fixed_in":["2.3.2-150400.3.9.1"],"sources":["osv"]},{"ecosystem":"SUSE:Linux Enterprise Server 16.0","package":"python-Flask","fixed_in":["3.1.1-160000.3.1"],"sources":["osv"]},{"ecosystem":"SUSE:Linux Enterprise Server for SAP applications 16.0","package":"python-Flask","fixed_in":["3.1.1-160000.3.1"],"sources":["osv"]},{"ecosystem":"Ubuntu:Pro:20.04:LTS","package":"flask","fixed_in":["1.1.1-2ubuntu0.1+esm1"],"sources":["osv"]},{"ecosystem":"Ubuntu:22.04:LTS","package":"flask","fixed_in":["2.0.1-2ubuntu1.2"],"sources":["osv"]},{"ecosystem":"Ubuntu:24.04:LTS","package":"flask","fixed_in":["3.0.2-1ubuntu1.1"],"sources":["osv"]},{"ecosystem":"openSUSE:Tumbleweed","package":"python-Flask","fixed_in":["3.1.3-1.1"],"sources":["osv"]}],"affected":[{"source":"ghsa","ecosystem":"PyPI","package":"flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.1.3"}]}]},{"source":"osv","ecosystem":"TuxCare:PyPI","package":"flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"2.2.5"},{"fixed":"2.2.5.post1+tuxcare"}]}],"versions":["2.2.5"]},{"source":"osv","ecosystem":"TuxCare:PyPI","package":"flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"1.1.4"},{"fixed":"1.1.4.post3+tuxcare"}]}],"versions":["1.1.4","1.1.4.post1+tuxcare","1.1.4.post2+tuxcare"]},{"source":"osv","ecosystem":"TuxCare:PyPI","package":"flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"1.1.2"},{"fixed":"1.1.2.post2+tuxcare"}]}],"versions":["1.1.2","1.1.2.post1+tuxcare"]},{"source":"osv","ecosystem":"TuxCare:PyPI","package":"flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0.12.5"},{"fixed":"0.12.5.post2+tuxcare"}]}],"versions":["0.12.5","0.12.5.post1+tuxcare"],"bundled":2},{"source":"osv","ecosystem":"TuxCare:PyPI","package":"flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"2.2.1"},{"fixed":"2.2.1.post2+tuxcare"}]}],"versions":["2.2.1","2.2.1.post1+tuxcare"],"bundled":2},{"source":"osv","ecosystem":"Debian:12","package":"flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.2.2-3","2.2.5-1","3.0.0-1","3.0.1-1","3.0.2-1","3.0.3-1","3.1.0-1","3.1.0-2","3.1.1-1","3.1.2-1","3.1.3-1","3.1.3-2","3.1.3-3","3.1.3-4"]},{"source":"osv","ecosystem":"Debian:13","package":"flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.1.1-1+deb13u1"}]}],"versions":["3.1.1-1"]},{"source":"osv","ecosystem":"Debian:14","package":"flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.1.3-1"}]}],"versions":["3.1.1-1","3.1.2-1"]},{"source":"osv","ecosystem":"PyPI","package":"flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.1.3"}]}],"versions":["0.1","0.10","0.10.1","0.11","0.11.1","0.12","0.12.1","0.12.2","0.12.3","0.12.4","0.12.5","0.2","0.3","0.3.1","0.4","0.5","0.5.1","0.5.2","0.6","0.6.1","0.7","0.7.1","0.7.2","0.8","0.8.1","0.9","1.0","1.0.1","1.0.2","1.0.3","1.0.4","1.1.0","1.1.1","1.1.2","1.1.3","1.1.4","2.0.0","2.0.0rc1","2.0.0rc2","2.0.1","2.0.2","2.0.3","2.1.0","2.1.1","2.1.2","2.1.3","2.2.0","2.2.1","2.2.2","2.2.3","2.2.4","2.2.5","2.3.0","2.3.1","2.3.2","2.3.3","3.0.0","3.0.1","3.0.2","3.0.3","3.1.0","3.1.1","3.1.2"]},{"source":"osv","ecosystem":"openEuler:24.03-LTS-SP3","package":"python-flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.2.5-2.oe2403sp3"}]}]},{"source":"osv","ecosystem":"openEuler:24.03-LTS","package":"python-flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.2.5-2.oe2403"}]}]},{"source":"osv","ecosystem":"openEuler:24.03-LTS-SP1","package":"python-flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.2.5-2.oe2403sp1"}]}]},{"source":"osv","ecosystem":"PyPI","package":"flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.1.3"}]}],"versions":["0.1","0.10","0.10.1","0.11","0.11.1","0.12","0.12.1","0.12.2","0.12.3","0.12.4","0.12.5","0.2","0.3","0.3.1","0.4","0.5","0.5.1","0.5.2","0.6","0.6.1","0.7","0.7.1","0.7.2","0.8","0.8.1","0.9","1.0","1.0.1","1.0.2","1.0.3","1.0.4","1.1.0","1.1.1","1.1.2","1.1.3","1.1.4","2.0.0","2.0.0rc1","2.0.0rc2","2.0.1","2.0.2","2.0.3","2.1.0","2.1.1","2.1.2","2.1.3","2.2.0","2.2.1","2.2.2","2.2.3","2.2.4","2.2.5","2.3.0","2.3.1","2.3.2","2.3.3","3.0.0","3.0.1","3.0.2","3.0.3","3.1.0","3.1.1","3.1.2"]},{"source":"osv","ecosystem":"Root:PyPI","package":"rootio-Flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.1.2+root.io.1"},{"fixed":"3.1.2+root.io.2"},{"fixed":"3.1.1+root.io.1"},{"fixed":"3.1.1+root.io.2"},{"fixed":"3.1.2+root.io.3"},{"fixed":"2.3.3+root.io.1"},{"fixed":"2.3.3+root.io.2"},{"fixed":"3.0.3+root.io.1"}]}]},{"source":"osv","ecosystem":"Root:PyPI","package":"Flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.1.1+aikido.2"},{"fixed":"3.1.2+aikido.3"}]}]},{"source":"osv","ecosystem":"SUSE:Linux Enterprise Module for Python 3 15 SP7","package":"python-Flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.3.2-150400.3.9.1"}]}]},{"source":"osv","ecosystem":"openSUSE:Leap 15.6","package":"python-Flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.3.2-150400.3.9.1"}]}]},{"source":"osv","ecosystem":"SUSE:Linux Enterprise Server 16.0","package":"python-Flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.1.1-160000.3.1"}]}]},{"source":"osv","ecosystem":"SUSE:Linux Enterprise Server for SAP applications 16.0","package":"python-Flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.1.1-160000.3.1"}]}]},{"source":"osv","ecosystem":"Ubuntu:16.04:LTS","package":"flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.10.1-2build2","0.10.1-2ubuntu0.1"]},{"source":"osv","ecosystem":"Ubuntu:18.04:LTS","package":"flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.12.2-2","0.12.2-3","0.12.2-3ubuntu0.1"]},{"source":"osv","ecosystem":"Ubuntu:Pro:20.04:LTS","package":"flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.1.1-2ubuntu0.1+esm1"}]}],"versions":["1.0.2-3","1.1.1-2","1.1.1-2ubuntu0.1"]},{"source":"osv","ecosystem":"Ubuntu:22.04:LTS","package":"flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.0.1-2ubuntu1.2"}]}],"versions":["1.1.2-2","2.0.1-2ubuntu1","2.0.1-2ubuntu1.1"]},{"source":"osv","ecosystem":"Ubuntu:24.04:LTS","package":"flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.0.2-1ubuntu1.1"}]}],"versions":["2.2.5-1ubuntu1","3.0.2-1ubuntu1"]},{"source":"osv","ecosystem":"Ubuntu:25.10","package":"flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.1.0-2ubuntu1","3.1.1-1ubuntu1","3.1.2-1ubuntu1"]},{"source":"osv","ecosystem":"Ubuntu:Pro:20.04:LTS","package":"flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.1.1-2ubuntu0.1+esm1"}]}],"versions":["1.0.2-3","1.1.1-2","1.1.1-2ubuntu0.1"]},{"source":"osv","ecosystem":"Ubuntu:22.04:LTS","package":"flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.0.1-2ubuntu1.2"}]}],"versions":["1.1.2-2","2.0.1-2ubuntu1","2.0.1-2ubuntu1.1"]},{"source":"osv","ecosystem":"Ubuntu:24.04:LTS","package":"flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.0.2-1ubuntu1.1"}]}],"versions":["2.2.5-1ubuntu1","3.0.2-1ubuntu1"]},{"source":"osv","ecosystem":"openSUSE:Tumbleweed","package":"python-Flask","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.1.3-1.1"}]}]}],"products":[{"vendor":"pallets","product":"flask"},{"vendor":"palletsprojects","product":"flask"}],"references":[{"url":"https://github.com/pallets/flask/security/advisories/GHSA-68rp-wp8r-4726","tags":["x_refsource_CONFIRM","Vendor Advisory","advisory","web","report"]},{"url":"https://github.com/pallets/flask/commit/089cb86dd22bff589a4eafb7ab8e42dc357623b4","tags":["x_refsource_MISC","Patch","fix","web"]},{"url":"https://github.com/pallets/flask/releases/tag/3.1.3","tags":["x_refsource_MISC","Product","Release Notes","web","advisory","report"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-27205","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-68rp-wp8r-4726"},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/27xxx/CVE-2026-27205.json","tags":["advisory"]},{"url":"https://security-tracker.debian.org/tracker/CVE-2026-27205","tags":["advisory"]},{"url":"https://github.com/pallets/flask","tags":["package"]},{"url":"https://www.openeuler.org/zh/security/security-bulletins/detail/?id=openEuler-SA-2026-2135","tags":["advisory"]},{"url":"https://www.openeuler.org/zh/security/security-bulletins/detail/?id=openEuler-SA-2026-2136","tags":["advisory"]},{"url":"https://www.openeuler.org/zh/security/security-bulletins/detail/?id=openEuler-SA-2026-2137","tags":["advisory"]},{"url":"https://www.suse.com/support/update/announcement/2026/suse-su-20260849-1/","tags":["advisory"]},{"url":"https://bugzilla.suse.com/1258700","tags":["report"]},{"url":"https://www.suse.com/security/cve/CVE-2026-27205","tags":["web"]},{"url":"https://www.suse.com/support/update/announcement/2026/suse-su-202622023-1/","tags":["advisory"]},{"url":"https://ubuntu.com/security/CVE-2026-27205","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-27205","tags":["report"]},{"url":"https://ubuntu.com/security/notices/USN-8104-1","tags":["advisory"]},{"url":"","tags":["advisory"]}],"sources":{"cve":[{"id":"CVE-2026-27205","title":"Flask session does not add `Vary: Cookie` header when accessed in some ways","description":"Flask is a web server gateway interface (WSGI) web application framework. In versions 3.1.2 and below, when the session object is accessed, Flask should set the Vary: Cookie header., resulting in a Use of Cache Containing Sensitive Information vulnerability. The logic instructs caches not to cache the response, as it may contain information specific to a logged in user. This is handled in most cases, but some forms of access such as the Python in operator were overlooked. The severity and risk depend on the application being hosted behind a caching proxy that doesn't ignore responses with cookies, not setting a Cache-Control header to mark pages as private or non-cacheable, and accessing the session in a way that only touches keys without reading values or mutating the session. The issue has been fixed in version 3.1.3.","status":"published","published":"2026-02-21T05:21:17.214Z","modified":"2026-02-24T19:03:11.374Z","cvss":[{"version":"4.0","score":2.3,"vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N","level":"low","assessor":"cna"}],"cwes":["CWE-524"],"updated_at":"2026-11-02T14:19:48.461833Z"}],"euvd":[{"id":"EUVD-2026-7731","description":"Flask is a web server gateway interface (WSGI) web application framework. In versions 3.1.2 and below, when the session object is accessed, Flask should set the Vary: Cookie header., resulting in a Use of Cache Containing Sensitive Information vulnerability. The logic instructs caches not to cache the response, as it may contain information specific to a logged in user. This is handled in most cases, but some forms of access such as the Python in operator were overlooked. The severity and risk depend on the application being hosted behind a caching proxy that doesn't ignore responses with cookies, not setting a Cache-Control header to mark pages as private or non-cacheable, and accessing the session in a way that only touches keys without reading values or mutating the session. The issue has been fixed in version 3.1.3.","status":"published","published":"2026-02-21T05:21:17Z","modified":"2026-02-24T19:03:11Z","cvss":[{"version":"4.0","score":2.3,"vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N","level":"low"}],"updated_at":"2026-11-02T19:48:29.551855Z"}],"ghsa":[{"id":"GHSA-68rp-wp8r-4726","title":"Flask session does not add `Vary: Cookie` header when accessed in some ways","description":"When the `session` object is accessed, Flask should set the `Vary: Cookie` header. This instructs caches not to cache the response, as it may contain information specific to a logged in user. This is handled in most cases, but some forms of access such as the Python `in` operator were overlooked.\n\nThe severity depends on the application's use of the session, and the cache's behavior regarding cookies. The risk depends on all these conditions being met.\n\n1. The application must be hosted behind a caching proxy that does not ignore responses with cookies.\n2. The application does not set a `Cache-Control` header to indicate that a page is private or should not be cached.\n3. The application accesses the session in a way that does not access the values, only the keys, and does not mutate the session.","status":"published","published":"2026-02-19T20:45:41Z","modified":"2026-02-23T22:28:06Z","cvss":[{"version":"4.0","score":2.3,"vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N","level":"low"}],"cwes":["CWE-524"],"updated_at":"2026-11-02T14:39:26.881079Z"}],"nvd":[{"id":"CVE-2026-27205","description":"Flask is a web server gateway interface (WSGI) web application framework. In versions 3.1.2 and below, when the session object is accessed, Flask should set the Vary: Cookie header., resulting in a Use of Cache Containing Sensitive Information vulnerability. The logic instructs caches not to cache the response, as it may contain information specific to a logged in user. This is handled in most cases, but some forms of access such as the Python in operator were overlooked. The severity and risk depend on the application being hosted behind a caching proxy that doesn't ignore responses with cookies, not setting a Cache-Control header to mark pages as private or non-cacheable, and accessing the session in a way that only touches keys without reading values or mutating the session. The issue has been fixed in version 3.1.3.","status":"published","published":"2026-02-21T06:17:00.91Z","modified":"2026-06-17T10:26:50.7Z","cvss":[{"version":"4.0","score":2.3,"vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","level":"low","assessor":"secondary"},{"version":"3.1","score":4.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N","level":"medium","assessor":"primary"}],"cwes":["CWE-524"],"updated_at":"2026-11-02T14:12:06.63895Z"}],"osv":[{"id":"CVE-2026-27205","title":"Flask session does not add `Vary: Cookie` header when accessed in some ways","description":"Flask is a web server gateway interface (WSGI) web application framework. In versions 3.1.2 and below, when the session object is accessed, Flask should set the Vary: Cookie header., resulting in a Use of Cache Containing Sensitive Information vulnerability. The logic instructs caches not to cache the response, as it may contain information specific to a logged in user. This is handled in most cases, but some forms of access such as the Python in operator were overlooked. The severity and risk depend on the application being hosted behind a caching proxy that doesn't ignore responses with cookies, not setting a Cache-Control header to mark pages as private or non-cacheable, and accessing the session in a way that only touches keys without reading values or mutating the session. The issue has been fixed in version 3.1.3.","status":"published","published":"2026-02-21T05:21:17.214Z","modified":"2026-10-28T02:30:22.002521921Z","cvss":[{"version":"4.0","score":2.3,"vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N","level":"low"}],"cwes":["CWE-524"],"updated_at":"2026-11-02T15:45:00.180685Z"},{"id":"DEBIAN-CVE-2026-27205","description":"Flask is a web server gateway interface (WSGI) web application framework. In versions 3.1.2 and below, when the session object is accessed, Flask should set the Vary: Cookie header., resulting in a Use of Cache Containing Sensitive Information vulnerability. The logic instructs caches not to cache the response, as it may contain information specific to a logged in user. This is handled in most cases, but some forms of access such as the Python in operator were overlooked. The severity and risk depend on the application being hosted behind a caching proxy that doesn't ignore responses with cookies, not setting a Cache-Control header to mark pages as private or non-cacheable, and accessing the session in a way that only touches keys without reading values or mutating the session. The issue has been fixed in version 3.1.3.","status":"published","published":"2026-02-21T06:17:00.91Z","modified":"2026-10-01T03:03:01.734591296Z","cvss":[{"version":"3.1","score":4.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N","level":"medium"}],"updated_at":"2026-11-02T15:45:53.877573Z"},{"id":"GHSA-68rp-wp8r-4726","title":"Flask session does not add `Vary: Cookie` header when accessed in some ways","description":"When the `session` object is accessed, Flask should set the `Vary: Cookie` header. This instructs caches not to cache the response, as it may contain information specific to a logged in user. This is handled in most cases, but some forms of access such as the Python `in` operator were overlooked.\n\nThe severity depends on the application's use of the session, and the cache's behavior regarding cookies. The risk depends on all these conditions being met.\n\n1. The application must be hosted behind a caching proxy that does not ignore responses with cookies.\n2. The application does not set a `Cache-Control` header to indicate that a page is private or should not be cached.\n3. The application accesses the session in a way that does not access the values, only the keys, and does not mutate the session.","status":"published","published":"2026-02-19T20:45:41Z","modified":"2026-09-10T03:49:54.35498159Z","cvss":[{"version":"4.0","score":2.3,"vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N","level":"low"}],"cwes":["CWE-524"],"updated_at":"2026-11-02T15:46:39.618611Z"},{"id":"OESA-2026-2135","title":"python-flask security update","description":"Flask is a lightweight WSGI web application framework. It is designed to make getting started quick and easy, with the ability to scale up to complex applications. It began as a simple wrapper around Werkzeug and Jinja and has become one of the most popular Python web application frameworks.\r\n\r\nSecurity Fix(es):\n\nFlask is a web server gateway interface (WSGI) web application framework. In versions 3.1.2 and below, when the session object is accessed, Flask should set the Vary: Cookie header., resulting in a Use of Cache Containing Sensitive Information vulnerability. The logic instructs caches not to cache the response, as it may contain information specific to a logged in user. This is handled in most cases, but some forms of access such as the Python in operator were overlooked. The severity and risk depend on the application being hosted behind a caching proxy that doesn\u0026apos;t ignore responses with cookies, not setting a Cache-Control header to mark pages as private or non-cacheable, and accessing the session in a way that only touches keys without reading values or mutating the session. The issue has been fixed in version 3.1.3.(CVE-2026-27205)","status":"published","published":"2026-05-03T11:11:07Z","modified":"2026-08-18T01:19:50.429573355Z","cvss":[{"version":"4.0","score":2.3,"vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","level":"low"}],"updated_at":"2026-11-02T15:52:46.087701Z"},{"id":"OESA-2026-2136","title":"python-flask security update","description":"Flask is a lightweight WSGI web application framework. It is designed to make getting started quick and easy, with the ability to scale up to complex applications. It began as a simple wrapper around Werkzeug and Jinja and has become one of the most popular Python web application frameworks.\r\n\r\nSecurity Fix(es):\n\nFlask is a web server gateway interface (WSGI) web application framework. In versions 3.1.2 and below, when the session object is accessed, Flask should set the Vary: Cookie header., resulting in a Use of Cache Containing Sensitive Information vulnerability. The logic instructs caches not to cache the response, as it may contain information specific to a logged in user. This is handled in most cases, but some forms of access such as the Python in operator were overlooked. The severity and risk depend on the application being hosted behind a caching proxy that doesn\u0026apos;t ignore responses with cookies, not setting a Cache-Control header to mark pages as private or non-cacheable, and accessing the session in a way that only touches keys without reading values or mutating the session. The issue has been fixed in version 3.1.3.(CVE-2026-27205)","status":"published","published":"2026-05-03T11:11:07Z","modified":"2026-08-18T01:19:56.524214356Z","cvss":[{"version":"4.0","score":2.3,"vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","level":"low"}],"updated_at":"2026-11-02T15:52:46.087701Z"},{"id":"OESA-2026-2137","title":"python-flask security update","description":"Flask is a lightweight WSGI web application framework. It is designed to make getting started quick and easy, with the ability to scale up to complex applications. It began as a simple wrapper around Werkzeug and Jinja and has become one of the most popular Python web application frameworks.\r\n\r\nSecurity Fix(es):\n\nFlask is a web server gateway interface (WSGI) web application framework. In versions 3.1.2 and below, when the session object is accessed, Flask should set the Vary: Cookie header., resulting in a Use of Cache Containing Sensitive Information vulnerability. The logic instructs caches not to cache the response, as it may contain information specific to a logged in user. This is handled in most cases, but some forms of access such as the Python in operator were overlooked. The severity and risk depend on the application being hosted behind a caching proxy that doesn\u0026apos;t ignore responses with cookies, not setting a Cache-Control header to mark pages as private or non-cacheable, and accessing the session in a way that only touches keys without reading values or mutating the session. The issue has been fixed in version 3.1.3.(CVE-2026-27205)","status":"published","published":"2026-05-03T11:11:07Z","modified":"2026-08-18T01:19:50.562859063Z","cvss":[{"version":"4.0","score":2.3,"vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","level":"low"}],"updated_at":"2026-11-02T15:52:46.087701Z"},{"id":"PYSEC-2026-2151","description":"Flask is a web server gateway interface (WSGI) web application framework. In versions 3.1.2 and below, when the session object is accessed, Flask should set the Vary: Cookie header., resulting in a Use of Cache Containing Sensitive Information vulnerability. The logic instructs caches not to cache the response, as it may contain information specific to a logged in user. This is handled in most cases, but some forms of access such as the Python in operator were overlooked. The severity and risk depend on the application being hosted behind a caching proxy that doesn't ignore responses with cookies, not setting a Cache-Control header to mark pages as private or non-cacheable, and accessing the session in a way that only touches keys without reading values or mutating the session. The issue has been fixed in version 3.1.3.","status":"published","published":"2026-02-21T06:17:00.91Z","modified":"2026-07-13T07:15:25.03384344Z","cvss":[{"version":"3.1","score":4.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N","level":"medium"}],"updated_at":"2026-11-02T15:52:55.537808Z"},{"id":"ROOT-APP-PYPI-CVE-2026-27205","title":"CVE-2026-27205 in rootio-Flask - Patched by Root","description":"Root has patched CVE-2026-27205 in the rootio-Flask package for Root:PyPI. Multiple fixed versions available.","status":"published","published":"2026-07-20T06:36:41Z","modified":"2026-07-20T13:15:10.325952296Z","cvss":[{"version":"3.1","score":4.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N","level":"medium"}],"updated_at":"2026-11-02T15:53:27.940619Z"},{"id":"UBUNTU-CVE-2026-27205","description":"Flask is a web server gateway interface (WSGI) web application framework. In versions 3.1.2 and below, when the session object is accessed, Flask should set the Vary: Cookie header., resulting in a Use of Cache Containing Sensitive Information vulnerability. The logic instructs caches not to cache the response, as it may contain information specific to a logged in user. This is handled in most cases, but some forms of access such as the Python in operator were overlooked. The severity and risk depend on the application being hosted behind a caching proxy that doesn't ignore responses with cookies, not setting a Cache-Control header to mark pages as private or non-cacheable, and accessing the session in a way that only touches keys without reading values or mutating the session. The issue has been fixed in version 3.1.3.","status":"published","published":"2026-02-21T06:17:00Z","modified":"2026-03-19T08:32:01.213639Z","cvss":[{"version":"4.0","score":2.3,"vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N","level":"low"},{"version":"3.1","score":4.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N","level":"medium"}],"updated_at":"2026-11-02T16:56:08.726452Z"},{"id":"CLSA-2026-1789727592","title":"TuxCare security update for flask (1 CVE)","description":"TuxCare rebuilt flask to address 1 CVE. Fixed in 2.2.5.post1+tuxcare.","status":"published","published":"2026-09-18T10:33:12Z","modified":"2026-10-15T09:48:01.998353295Z","updated_at":"2026-11-02T15:43:48.28229Z"},{"id":"CLSA-2026-1789986000","title":"TuxCare security update for flask (1 CVE)","description":"TuxCare rebuilt flask to address 1 CVE. Fixed in 1.1.4.post3+tuxcare.","status":"published","published":"2026-09-21T10:20:00Z","modified":"2026-10-15T09:48:01.766675719Z","updated_at":"2026-11-02T15:43:48.28229Z"},{"id":"CLSA-2026-1789986625","title":"TuxCare security update for flask (1 CVE)","description":"TuxCare rebuilt flask to address 1 CVE. Fixed in 1.1.2.post2+tuxcare.","status":"published","published":"2026-09-21T10:30:25Z","modified":"2026-10-15T09:48:01.78990628Z","updated_at":"2026-11-02T15:43:48.28229Z"},{"id":"CLSA-2026-1789986626","title":"TuxCare security update for flask (2 CVEs)","description":"TuxCare rebuilt flask to address 2 CVEs. Fixed in 0.12.5.post2+tuxcare.","status":"published","published":"2026-09-21T10:30:25Z","modified":"2026-10-15T09:48:01.79984282Z","updated_at":"2026-11-02T15:43:48.28229Z"},{"id":"CLSA-2026-1789987201","title":"TuxCare security update for flask (2 CVEs)","description":"TuxCare rebuilt flask to address 2 CVEs. Fixed in 2.2.1.post2+tuxcare.","status":"published","published":"2026-09-21T10:40:01Z","modified":"2026-10-15T09:48:01.765865819Z","updated_at":"2026-11-02T15:43:48.28229Z"},{"id":"openSUSE-SU-2026:10264-1","title":"python311-Flask-3.1.3-1.1 on GA media","description":"These are all security issues fixed in the python311-Flask-3.1.3-1.1 package on the GA media of openSUSE Tumbleweed.","status":"published","published":"2026-02-26T00:00:00Z","modified":"2026-03-23T04:54:37.695549Z","updated_at":"2026-11-02T16:58:38.101535Z"},{"id":"openSUSE-SU-2026:20885-1","title":"Security update for python-Flask","description":"This update for python-Flask fixes the following issue:\n\n- CVE-2026-27205: information disclosure due to Flask session not adding the `Vary: Cookie` header (bsc#1258700).\n","status":"published","published":"2026-06-02T17:26:26Z","modified":"2026-06-04T09:00:09.187965179Z","updated_at":"2026-11-02T16:58:41.885092Z"},{"id":"SUSE-SU-2026:0849-1","title":"Security update for python-Flask","description":"This update for python-Flask fixes the following issue:\n\n- CVE-2026-27205: information disclosure due to Flask session not adding the `Vary: Cookie` header (bsc#1258700).\n","status":"published","published":"2026-03-09T10:13:40Z","modified":"2026-03-10T12:45:06.468569Z","updated_at":"2026-11-02T15:54:01.262144Z"},{"id":"SUSE-SU-2026:22023-1","title":"Security update for python-Flask","description":"This update for python-Flask fixes the following issue:\n\n- CVE-2026-27205: information disclosure due to Flask session not adding the `Vary: Cookie` header (bsc#1258700).\n","status":"published","published":"2026-06-02T17:26:47Z","modified":"2026-06-09T18:24:20.415801681Z","updated_at":"2026-11-02T15:54:02.654057Z"},{"id":"USN-8104-1","title":"flask vulnerability","description":"Shourya Jaiswal discovered that Flask did not correctly mark certain web\nresponses as user-specific. A remote attacker could possibly use this\nissue to obtain sensitive information.","status":"published","published":"2026-03-18T03:18:47Z","modified":"2026-04-27T18:38:01.028568Z","updated_at":"2026-11-02T16:58:22.951676Z"}]}}