{"id":"CVE-2026-116577","aliases":["AZL-111739","CLSA-2026-1793872514","CLSA-2026-1794218750","DEBIAN-CVE-2026-116577","EUVD-2026-110318","GHSA-pcg2-g6cj-q92c","OESA-2026-4798","OESA-2026-4799","OESA-2026-4800","UBUNTU-CVE-2026-116577","openSUSE-SU-2026:12440-1"],"status":"published","title":"Tornado: Quadratic CPU usage when parsing HTTP headers with line folding","description":"Tornado is a Python web framework and asynchronous networking library. Prior to 6.6, Tornado's HTTP header parser accepts obsolete line folding and repeatedly concatenates short continuation lines, causing quadratic CPU consumption on the IOLoop thread. An unauthenticated client can submit a header block containing many obsolete line-folding continuations before application code runs, blocking other connections served by the process. The cost grows with max_header_size, and only availability is affected. This issue is fixed in version 6.6.","severity":{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-12","score":0.00384,"percentile":0.32912,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-407","CWE-770"],"published":"2026-10-26T20:20:22Z","modified":"2026-11-12T17:25:21Z","fixes":[{"ecosystem":"PyPI","package":"tornado","fixed_in":["6.6"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"PyPI","package":"tornado","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.6"}]}]},{"source":"osv","ecosystem":"Azure Linux:3","package":"python-tornado","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"6.3.3-11"}]}]},{"source":"osv","ecosystem":"TuxCare:PyPI","package":"tornado","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"6.1"},{"fixed":"6.1.0.post11+tuxcare"}]}],"versions":["6.1","6.1.0.post1+tuxcare","6.1.0.post10+tuxcare","6.1.0.post2+tuxcare","6.1.0.post3+tuxcare","6.1.0.post4+tuxcare","6.1.0.post5+tuxcare","6.1.0.post6+tuxcare","6.1.0.post7+tuxcare","6.1.0.post8+tuxcare","6.1.0.post9+tuxcare"],"bundled":3},{"source":"osv","ecosystem":"TuxCare:PyPI","package":"tornado","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"5.1.1"},{"fixed":"5.1.1.post7+tuxcare"}]}],"versions":["5.1.1","5.1.1.post1+tuxcare","5.1.1.post2+tuxcare","5.1.1.post3+tuxcare","5.1.1.post4+tuxcare","5.1.1.post5+tuxcare","5.1.1.post6+tuxcare"],"bundled":3},{"source":"osv","ecosystem":"Debian:12","package":"python-tornado","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["6.2.0-3","6.2.0-3+deb12u1","6.2.0-3+deb12u2","6.2.0-3+deb12u3","6.2.0-3+deb12u4","6.3.2-1","6.4.0-1","6.4.0-2","6.4.1-1","6.4.1-2","6.4.1-3","6.4.2-1","6.4.2-2","6.4.2-3","6.5.2-1","6.5.2-2","6.5.2-3","6.5.4-0.1","6.5.4-1","6.5.5-1","6.5.5-2","6.5.5-3","6.5.5-4","6.5.5-5","6.6.0-1"]},{"source":"osv","ecosystem":"Debian:13","package":"python-tornado","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["6.4.2-3","6.4.2-3+deb13u1","6.4.2-3+deb13u2","6.5.2-1","6.5.2-2","6.5.2-3","6.5.4-0.1","6.5.4-1","6.5.5-1","6.5.5-2","6.5.5-3","6.5.5-4","6.5.5-5","6.6.0-1"]},{"source":"osv","ecosystem":"Debian:14","package":"python-tornado","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["6.4.2-3","6.5.2-1","6.5.2-2","6.5.2-3","6.5.4-0.1","6.5.4-1","6.5.5-1","6.5.5-2","6.5.5-3","6.5.5-4","6.5.5-5","6.6.0-1"]},{"source":"osv","ecosystem":"PyPI","package":"tornado","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.6"}]}],"versions":["0.2","1.0","1.1","1.1.1","1.2","1.2.1","2.0","2.1","2.1.1","2.2","2.2.1","2.3","2.4","2.4.1","3.0","3.0.1","3.0.2","3.1","3.1.1","3.2","3.2.1","3.2.2","4.0","4.0.1","4.0.2","4.1","4.1b2","4.2","4.2.1","4.2b1","4.3","4.3b1","4.3b2","4.4","4.4.1","4.4.2","4.4.3","4.4b1","4.5","4.5.1","4.5.2","4.5.3","4.5b1","4.5b2","5.0","5.0.1","5.0.2","5.0a1","5.0b1","5.1","5.1.1","5.1b1","6.0","6.0.1","6.0.2","6.0.3","6.0.4","6.0a1","6.0b1","6.1","6.1b1","6.1b2","6.2","6.2b1","6.2b2","6.3","6.3.1","6.3.2","6.3.3","6.3b1","6.4","6.4.1","6.4.2","6.4b1","6.5","6.5.1","6.5.10","6.5.2","6.5.3","6.5.4","6.5.5","6.5.6","6.5.7","6.5.8","6.5.9","6.5b1","6.6a1","6.6b1","6.6rc1"]},{"source":"osv","ecosystem":"openEuler:24.03-LTS-SP1","package":"python-tornado","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.6-1.oe2403sp1"}]}],"bundled":3},{"source":"osv","ecosystem":"openEuler:24.03-LTS-SP3","package":"python-tornado","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.6-1.oe2403sp3"}]}],"bundled":3},{"source":"osv","ecosystem":"openEuler:24.03-LTS-SP4","package":"python-tornado","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.6-1.oe2403sp4"}]}],"bundled":3},{"source":"osv","ecosystem":"Ubuntu:Pro:16.04:LTS","package":"python-tornado","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["4.2.1-1ubuntu2","4.2.1-1ubuntu3","4.2.1-1ubuntu3.1","4.2.1-1ubuntu3.1+esm1","4.2.1-1ubuntu3.1+esm2","4.2.1-1ubuntu3.1+esm3","4.2.1-1ubuntu3.1+esm4","4.2.1-1ubuntu3.1+esm5","4.2.1-1ubuntu3.1+esm6"]},{"source":"osv","ecosystem":"Ubuntu:Pro:18.04:LTS","package":"python-tornado","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["4.5.1-2.1~build2","4.5.2-1","4.5.3-1","4.5.3-1ubuntu0.1","4.5.3-1ubuntu0.2","4.5.3-1ubuntu0.2+esm1","4.5.3-1ubuntu0.2+esm2","4.5.3-1ubuntu0.2+esm3","4.5.3-1ubuntu0.2+esm4","4.5.3-1ubuntu0.2+esm5","4.5.3-1ubuntu0.2+esm6"]},{"source":"osv","ecosystem":"Ubuntu:Pro:20.04:LTS","package":"python-tornado","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["5.1.1-4ubuntu1","5.1.1-4ubuntu5","6.0.3+really5.1.1-2","6.0.3+really5.1.1-2build1","6.0.3+really5.1.1-2build2","6.0.3+really5.1.1-3","6.0.3+really5.1.1-3ubuntu0.1~esm1","6.0.3+really5.1.1-3ubuntu0.1~esm3","6.0.3+really5.1.1-3ubuntu0.1~esm5","6.0.3+really5.1.1-3ubuntu0.1~esm7","6.0.3+really5.1.1-3ubuntu0.1~esm8","6.0.3+really5.1.1-3ubuntu0.1~esm9"]},{"source":"osv","ecosystem":"Ubuntu:Pro:22.04:LTS","package":"python-tornado","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["6.1.0-1build1","6.1.0-2","6.1.0-3","6.1.0-3build1","6.1.0-3ubuntu0.1~esm1","6.1.0-3ubuntu0.1~esm2","6.1.0-3ubuntu0.1~esm4","6.1.0-3ubuntu0.1~esm5","6.1.0-3ubuntu0.1~esm6","6.1.0-3ubuntu0.1~esm7","6.1.0-3ubuntu0.1~esm8"]},{"source":"osv","ecosystem":"Ubuntu:24.04:LTS","package":"python-tornado","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["6.3.2-1","6.4.0-0ubuntu1","6.4.0-1","6.4.0-1build1","6.4.0-1ubuntu0.1","6.4.0-1ubuntu0.2","6.4.0-1ubuntu0.4","6.4.0-1ubuntu0.5","6.4.0-1ubuntu0.6","6.4.0-1ubuntu0.7","6.4.0-1ubuntu0.8"]},{"source":"osv","ecosystem":"Ubuntu:26.10","package":"python-tornado","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["6.5.4-0.1","6.5.5-2","6.5.5-4","6.5.5-5","6.5.5-5ubuntu1.1","6.5.5-5ubuntu1.2","6.5.5-5ubuntu1.3"]},{"source":"osv","ecosystem":"Ubuntu:26.04:LTS","package":"python-tornado","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["6.4.2-3","6.5.2-3","6.5.4-0.1","6.5.4-0.1ubuntu0.1","6.5.4-0.1ubuntu0.2","6.5.4-0.1ubuntu0.3","6.5.4-0.1ubuntu0.4"]},{"source":"osv","ecosystem":"openSUSE:Tumbleweed","package":"python-tornado6","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.6-1.1"}]}],"bundled":3}],"products":[{"vendor":"tornadoweb","product":"tornado"}],"references":[{"url":"https://github.com/tornadoweb/tornado/security/advisories/GHSA-pcg2-g6cj-q92c","tags":["x_refsource_CONFIRM","advisory","web","report"]},{"url":"https://github.com/tornadoweb/tornado/pull/3765","tags":["x_refsource_MISC","fix","web","report"]},{"url":"https://github.com/tornadoweb/tornado/commit/1b7a1dc9f340f52de929852e8125aa12f25297c9","tags":["x_refsource_MISC","fix","web","report"]},{"url":"https://github.com/tornadoweb/tornado/releases/tag/v6.6.0","tags":["x_refsource_MISC","web","report"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-116577","tags":["web","advisory"]},{"url":"https://github.com/advisories/GHSA-pcg2-g6cj-q92c"},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/116xxx/CVE-2026-116577.json","tags":["advisory"]},{"url":"https://security-tracker.debian.org/tracker/CVE-2026-116577","tags":["advisory"]},{"url":"https://github.com/tornadoweb/tornado","tags":["package"]},{"url":"https://www.openeuler.org/zh/security/security-bulletins/detail/?id=openEuler-SA-2026-4798","tags":["advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-115927","tags":["advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-116578","tags":["advisory"]},{"url":"https://www.openeuler.org/zh/security/security-bulletins/detail/?id=openEuler-SA-2026-4799","tags":["advisory"]},{"url":"https://www.openeuler.org/zh/security/security-bulletins/detail/?id=openEuler-SA-2026-4800","tags":["advisory"]},{"url":"https://ubuntu.com/security/CVE-2026-116577","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-116577","tags":["report"]},{"url":"","tags":["advisory"]},{"url":"https://www.suse.com/security/cve/CVE-2026-115927","tags":["web"]},{"url":"https://www.suse.com/security/cve/CVE-2026-116577","tags":["web"]},{"url":"https://www.suse.com/security/cve/CVE-2026-116578","tags":["web"]}],"sources":{"cve":[{"id":"CVE-2026-116577","title":"Tornado: Quadratic CPU usage when parsing HTTP headers with line folding","description":"Tornado is a Python web framework and asynchronous networking library. Prior to 6.6, Tornado's HTTP header parser accepts obsolete line folding and repeatedly concatenates short continuation lines, causing quadratic CPU consumption on the IOLoop thread. An unauthenticated client can submit a header block containing many obsolete line-folding continuations before application code runs, blocking other connections served by the process. The cost grows with max_header_size, and only availability is affected. This issue is fixed in version 6.6.","status":"published","published":"2026-10-26T20:20:22.104Z","modified":"2026-10-31T01:48:45.286Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium","assessor":"cna"}],"cwes":["CWE-407","CWE-770"],"updated_at":"2026-11-02T14:20:03.4818Z"}],"euvd":[{"id":"EUVD-2026-110318","description":"Tornado is a Python web framework and asynchronous networking library. Prior to 6.6, Tornado's HTTP header parser accepts obsolete line folding and repeatedly concatenates short continuation lines, causing quadratic CPU consumption on the IOLoop thread. An unauthenticated client can submit a header block containing many obsolete line-folding continuations before application code runs, blocking other connections served by the process. The cost grows with max_header_size, and only availability is affected. This issue is fixed in version 6.6.","status":"published","published":"2026-10-26T20:20:22Z","modified":"2026-10-31T01:48:45Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium"}],"updated_at":"2026-11-02T16:59:01.198534Z"}],"ghsa":[{"id":"GHSA-pcg2-g6cj-q92c","title":"Tornado: Quadratic CPU usage when parsing HTTP headers with line folding","description":"### Summary\n\nTornado's HTTP header parser takes quadratic time (O(n²)) when a header value is continued across many \"obsolete line folding\" (obs-fold) lines. An unauthenticated attacker can send a request whose header block is mostly short continuation lines. Parsing it uses a large amount of CPU on the IOLoop thread and blocks every other connection that process is serving.\n\nThis issue is closely related to CVE-2025-67725 (GHSA-c98p-7wgm-6p64). The fix for that advisory covered repeated headers but not line-folded continuations.\n\n### Impact\n\nAll Tornado HTTP servers are affected. Header parsing runs before any application code, so no authentication or particular handler is required.\n\nHow bad it gets depends on `max_header_size`:\n\n- **Default (64 KB):** each malicious request blocks the event loop for tens of milliseconds. Repeated requests can degrade service.\n- **Raised `max_header_size`:** the cost grows with the square of the header size. A single 1 MB request can block the process for several seconds.\n\nOnly availability is affected. Confidentiality and integrity are not.\n\n### Patches\n\nFixed in Tornado 6.6 by removing support for obsolete line folding completely; header lines that begin with whitespace are now rejected.\n\n### Workarounds\n\n- Keep `max_header_size` at its default value or lower it. This limits the impact but doesn't remove it.\n- Run Tornado behind a reverse proxy that rejects or normalizes obsolete line folding before forwarding requests.\n\n### Credit\n\nReported by @manus-pi.","status":"published","published":"2026-10-28T22:43:41Z","modified":"2026-10-28T22:43:44Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium"}],"cwes":["CWE-407","CWE-770"],"updated_at":"2026-11-02T14:41:39.926569Z"}],"nvd":[{"id":"CVE-2026-116577","description":"Tornado is a Python web framework and asynchronous networking library. Prior to 6.6, Tornado's HTTP header parser accepts obsolete line folding and repeatedly concatenates short continuation lines, causing quadratic CPU consumption on the IOLoop thread. An unauthenticated client can submit a header block containing many obsolete line-folding continuations before application code runs, blocking other connections served by the process. The cost grows with max_header_size, and only availability is affected. This issue is fixed in version 6.6.","status":"published","published":"2026-10-26T21:18:14.087Z","modified":"2026-10-31T02:17:32.873Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium","assessor":"secondary"}],"cwes":["CWE-407","CWE-770"],"updated_at":"2026-11-02T14:13:03.746397Z"}],"osv":[{"id":"CVE-2026-116577","title":"Tornado: Quadratic CPU usage when parsing HTTP headers with line folding","description":"Tornado is a Python web framework and asynchronous networking library. Prior to 6.6, Tornado's HTTP header parser accepts obsolete line folding and repeatedly concatenates short continuation lines, causing quadratic CPU consumption on the IOLoop thread. An unauthenticated client can submit a header block containing many obsolete line-folding continuations before application code runs, blocking other connections served by the process. The cost grows with max_header_size, and only availability is affected. This issue is fixed in version 6.6.","status":"published","published":"2026-10-26T20:20:22.104Z","modified":"2026-11-06T17:27:22.630780255Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium"}],"cwes":["CWE-407","CWE-770"],"updated_at":"2026-11-06T18:02:56.921874Z"},{"id":"DEBIAN-CVE-2026-116577","description":"Tornado is a Python web framework and asynchronous networking library. Prior to 6.6, Tornado's HTTP header parser accepts obsolete line folding and repeatedly concatenates short continuation lines, causing quadratic CPU consumption on the IOLoop thread. An unauthenticated client can submit a header block containing many obsolete line-folding continuations before application code runs, blocking other connections served by the process. The cost grows with max_header_size, and only availability is affected. This issue is fixed in version 6.6.","status":"published","published":"2026-10-26T21:18:14.087Z","modified":"2026-10-31T10:01:11.707839485Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium"}],"updated_at":"2026-11-02T15:45:50.923612Z"},{"id":"GHSA-pcg2-g6cj-q92c","title":"Tornado: Quadratic CPU usage when parsing HTTP headers with line folding","description":"### Summary\n\nTornado's HTTP header parser takes quadratic time (O(n²)) when a header value is continued across many \"obsolete line folding\" (obs-fold) lines. An unauthenticated attacker can send a request whose header block is mostly short continuation lines. Parsing it uses a large amount of CPU on the IOLoop thread and blocks every other connection that process is serving.\n\nThis issue is closely related to CVE-2025-67725 (GHSA-c98p-7wgm-6p64). The fix for that advisory covered repeated headers but not line-folded continuations.\n\n### Impact\n\nAll Tornado HTTP servers are affected. Header parsing runs before any application code, so no authentication or particular handler is required.\n\nHow bad it gets depends on `max_header_size`:\n\n- **Default (64 KB):** each malicious request blocks the event loop for tens of milliseconds. Repeated requests can degrade service.\n- **Raised `max_header_size`:** the cost grows with the square of the header size. A single 1 MB request can block the process for several seconds.\n\nOnly availability is affected. Confidentiality and integrity are not.\n\n### Patches\n\nFixed in Tornado 6.6 by removing support for obsolete line folding completely; header lines that begin with whitespace are now rejected.\n\n### Workarounds\n\n- Keep `max_header_size` at its default value or lower it. This limits the impact but doesn't remove it.\n- Run Tornado behind a reverse proxy that rejects or normalizes obsolete line folding before forwarding requests.\n\n### Credit\n\nReported by @manus-pi.","status":"published","published":"2026-10-28T22:43:41Z","modified":"2026-10-28T23:00:04.070057045Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium"}],"cwes":["CWE-407","CWE-770"],"updated_at":"2026-11-02T15:46:52.891208Z"},{"id":"OESA-2026-4798","title":"python-tornado security update","description":"Tornado is a Python web framework and asynchronous networking library, originally developed at FriendFeed. By using non-blocking network I/O, Tornado can scale to tens of thousands of open connections, making it ideal for long polling, WebSockets, and other applications that require a long-lived connection to each user.\r\n\r\nSecurity Fix(es):\n\nTornado is a Python web framework and asynchronous networking library. Prior to 6.6.0, Tornado decodes HTTP/1.1 chunked transfer encoding by processing body data that has already arrived without yielding to the event loop. A remote unauthenticated peer can send millions of one-byte chunks to monopolize the process event loop and stall every other connection served by that process, while lowering max_body_size only limits the duration of each request. For handlers that do not use @stream_request_body, retaining each chunk as a separate object can consume roughly twenty times the received body size, and SimpleAsyncHTTPClient has the same event-loop behavior when reading a response from a malicious server. This issue is fixed in version 6.6.0.(CVE-2026-115927)\n\nTornado is a Python web framework and asynchronous networking library. Prior to 6.6, Tornado\u0026apos;s HTTP header parser accepts obsolete line folding and repeatedly concatenates short continuation lines, causing quadratic CPU consumption on the IOLoop thread. An unauthenticated client can submit a header block containing many obsolete line-folding continuations before application code runs, blocking other connections served by the process. The cost grows with max_header_size, and only availability is affected. This issue is fixed in version 6.6.(CVE-2026-116577)\n\nTornado is a Python web framework and asynchronous networking library. Prior to 6.6, tornado.web.RedirectHandler URL templates can place regex-capture substitutions where crafted request paths change the redirect scheme or network location. Affected placements include substitutions at the start of a path, directly after a fixed host, or at the beginning of the template, including protocol-relative, absolute, backslash, encoded, host-extension, and user-info variants interpreted by browsers as attacker-controlled destinations. Static templates and substitutions after a fixed host followed by a slash are not affected. An attacker can use the resulting open redirect on the application\u0026apos;s domain for phishing. This issue is fixed in version 6.6.(CVE-2026-116578)","status":"published","published":"2026-11-11T12:26:16Z","modified":"2026-11-11T12:45:07.500813004Z","cvss":[{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium"}],"updated_at":"2026-11-11T13:08:46.301371Z"},{"id":"OESA-2026-4799","title":"python-tornado security update","description":"Tornado is a Python web framework and asynchronous networking library, originally developed at FriendFeed. By using non-blocking network I/O, Tornado can scale to tens of thousands of open connections, making it ideal for long polling, WebSockets, and other applications that require a long-lived connection to each user.\r\n\r\nSecurity Fix(es):\n\nTornado is a Python web framework and asynchronous networking library. Prior to 6.6.0, Tornado decodes HTTP/1.1 chunked transfer encoding by processing body data that has already arrived without yielding to the event loop. A remote unauthenticated peer can send millions of one-byte chunks to monopolize the process event loop and stall every other connection served by that process, while lowering max_body_size only limits the duration of each request. For handlers that do not use @stream_request_body, retaining each chunk as a separate object can consume roughly twenty times the received body size, and SimpleAsyncHTTPClient has the same event-loop behavior when reading a response from a malicious server. This issue is fixed in version 6.6.0.(CVE-2026-115927)\n\nTornado is a Python web framework and asynchronous networking library. Prior to 6.6, Tornado\u0026apos;s HTTP header parser accepts obsolete line folding and repeatedly concatenates short continuation lines, causing quadratic CPU consumption on the IOLoop thread. An unauthenticated client can submit a header block containing many obsolete line-folding continuations before application code runs, blocking other connections served by the process. The cost grows with max_header_size, and only availability is affected. This issue is fixed in version 6.6.(CVE-2026-116577)\n\nTornado is a Python web framework and asynchronous networking library. Prior to 6.6, tornado.web.RedirectHandler URL templates can place regex-capture substitutions where crafted request paths change the redirect scheme or network location. Affected placements include substitutions at the start of a path, directly after a fixed host, or at the beginning of the template, including protocol-relative, absolute, backslash, encoded, host-extension, and user-info variants interpreted by browsers as attacker-controlled destinations. Static templates and substitutions after a fixed host followed by a slash are not affected. An attacker can use the resulting open redirect on the application\u0026apos;s domain for phishing. This issue is fixed in version 6.6.(CVE-2026-116578)","status":"published","published":"2026-11-11T12:26:17Z","modified":"2026-11-11T12:45:07.504282553Z","cvss":[{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium"}],"updated_at":"2026-11-11T13:08:46.301371Z"},{"id":"OESA-2026-4800","title":"python-tornado security update","description":"Tornado is a Python web framework and asynchronous networking library, originally developed at FriendFeed. By using non-blocking network I/O, Tornado can scale to tens of thousands of open connections, making it ideal for long polling, WebSockets, and other applications that require a long-lived connection to each user.\r\n\r\nSecurity Fix(es):\n\nTornado is a Python web framework and asynchronous networking library. Prior to 6.6.0, Tornado decodes HTTP/1.1 chunked transfer encoding by processing body data that has already arrived without yielding to the event loop. A remote unauthenticated peer can send millions of one-byte chunks to monopolize the process event loop and stall every other connection served by that process, while lowering max_body_size only limits the duration of each request. For handlers that do not use @stream_request_body, retaining each chunk as a separate object can consume roughly twenty times the received body size, and SimpleAsyncHTTPClient has the same event-loop behavior when reading a response from a malicious server. This issue is fixed in version 6.6.0.(CVE-2026-115927)\n\nTornado is a Python web framework and asynchronous networking library. Prior to 6.6, Tornado\u0026apos;s HTTP header parser accepts obsolete line folding and repeatedly concatenates short continuation lines, causing quadratic CPU consumption on the IOLoop thread. An unauthenticated client can submit a header block containing many obsolete line-folding continuations before application code runs, blocking other connections served by the process. The cost grows with max_header_size, and only availability is affected. This issue is fixed in version 6.6.(CVE-2026-116577)\n\nTornado is a Python web framework and asynchronous networking library. Prior to 6.6, tornado.web.RedirectHandler URL templates can place regex-capture substitutions where crafted request paths change the redirect scheme or network location. Affected placements include substitutions at the start of a path, directly after a fixed host, or at the beginning of the template, including protocol-relative, absolute, backslash, encoded, host-extension, and user-info variants interpreted by browsers as attacker-controlled destinations. Static templates and substitutions after a fixed host followed by a slash are not affected. An attacker can use the resulting open redirect on the application\u0026apos;s domain for phishing. This issue is fixed in version 6.6.(CVE-2026-116578)","status":"published","published":"2026-11-11T12:26:17Z","modified":"2026-11-11T12:45:06.745550266Z","cvss":[{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium"}],"updated_at":"2026-11-11T13:08:46.301371Z"},{"id":"UBUNTU-CVE-2026-116577","description":"Tornado is a Python web framework and asynchronous networking library. Prior to 6.6, Tornado's HTTP header parser accepts obsolete line folding and repeatedly concatenates short continuation lines, causing quadratic CPU consumption on the IOLoop thread. An unauthenticated client can submit a header block containing many obsolete line-folding continuations before application code runs, blocking other connections served by the process. The cost grows with max_header_size, and only availability is affected. This issue is fixed in version 6.6.","status":"published","published":"2026-10-26T21:18:00Z","modified":"2026-11-12T17:25:21.224719943Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium"}],"updated_at":"2026-11-12T18:05:20.578263Z"},{"id":"AZL-111739","title":"CVE-2026-116577 affecting package python-tornado 6.3.3-11","description":"Tornado is a Python web framework and asynchronous networking library. Prior to 6.6, Tornado's HTTP header parser accepts obsolete line folding and repeatedly concatenates short continuation lines, causing quadratic CPU consumption on the IOLoop thread. An unauthenticated client can submit a header block containing many obsolete line-folding continuations before application code runs, blocking other connections served by the process. The cost grows with max_header_size, and only availability is affected. This issue is fixed in version 6.6.","status":"published","published":"2026-10-26T21:18:14Z","modified":"2026-11-05T05:36:30Z","updated_at":"2026-11-05T16:41:18.705965Z"},{"id":"CLSA-2026-1793872514","title":"TuxCare security update for tornado (3 CVEs)","description":"TuxCare rebuilt tornado to address 3 CVEs. Fixed in 6.1.0.post11+tuxcare.","status":"published","published":"2026-11-05T10:55:15Z","modified":"2026-11-05T13:15:16.678127586Z","updated_at":"2026-11-05T13:30:00.949926Z"},{"id":"CLSA-2026-1794218750","title":"TuxCare security update for tornado (3 CVEs)","description":"TuxCare rebuilt tornado to address 3 CVEs. Fixed in 5.1.1.post7+tuxcare.","status":"published","published":"2026-11-09T11:05:51Z","modified":"2026-11-09T19:15:14.554614128Z","updated_at":"2026-11-09T19:38:09.278998Z"},{"id":"openSUSE-SU-2026:12440-1","title":"python313-tornado6-6.6-1.1 on GA media","description":"These are all security issues fixed in the python313-tornado6-6.6-1.1 package on the GA media of openSUSE Tumbleweed.","status":"published","published":"2026-11-05T00:00:00Z","modified":"2026-11-06T17:23:10.698741151Z","updated_at":"2026-11-06T18:05:03.243497Z"}]}}