{"id":"CVE-2021-20236","aliases":["BELL-CVE-2021-20236","DEBIAN-CVE-2021-20236","EUVD-2021-7675","GHSA-4j25-p3vq-p264","GHSA-qq65-x72m-9wr8","JLSEC-2026-516","UBUNTU-CVE-2021-20236"],"status":"published","title":"A flaw was found in the ZeroMQ server in versions before 4.3.3. This flaw allows a malicious...","description":"A flaw was found in the ZeroMQ server in versions before 4.3.3. This flaw allows a malicious client to cause a stack buffer overflow on the server by sending crafted topic subscription requests and then unsubscribing. The highest threat from this vulnerability is to confidentiality, integrity, as well as system availability.","severity":{"version":"3.1","score":9.8,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"critical","assessor":"primary","from":"nvd"},"epss":{"day":"2026-11-10","score":0.01868,"percentile":0.79497,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-120","CWE-787"],"published":"2021-05-28T10:42:19Z","modified":"2026-11-09T10:30:25Z","fixes":[{"ecosystem":"Debian:12","package":"zeromq3","fixed_in":["4.3.3-1"],"sources":["osv"]},{"ecosystem":"Debian:13","package":"zeromq3","fixed_in":["4.3.3-1"],"sources":["osv"]},{"ecosystem":"Debian:14","package":"zeromq3","fixed_in":["4.3.3-1"],"sources":["osv"]},{"ecosystem":"Julia","package":"ZeroMQ_jll","fixed_in":["4.3.4+0"],"sources":["osv"]}],"affected":[{"source":"osv","ecosystem":"Debian:12","package":"zeromq3","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.3.3-1"}]}]},{"source":"osv","ecosystem":"Debian:13","package":"zeromq3","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.3.3-1"}]}]},{"source":"osv","ecosystem":"Debian:14","package":"zeromq3","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.3.3-1"}]}]},{"source":"osv","ecosystem":"Julia","package":"ZeroMQ_jll","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"4.3.4+0"}]}]},{"source":"osv","ecosystem":"Ubuntu:Pro:14.04:LTS","package":"zeromq3","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.2.3+dfsg-2","3.2.4+dfsg-1","3.2.4+dfsg-2","3.2.4+dfsg-3","3.2.4+dfsg-4","4.0.3+dfsg-1","4.0.4+dfsg-2","4.0.4+dfsg-2ubuntu0.1","4.0.4+dfsg-2ubuntu0.1+esm1","4.0.4+dfsg-2ubuntu0.1+esm2","4.0.4+dfsg-2ubuntu0.1+esm3"]},{"source":"osv","ecosystem":"Ubuntu:Pro:16.04:LTS","package":"zeromq3","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["4.0.5+dfsg-3ubuntu1~gcc5.1","4.0.5+dfsg-3ubuntu2","4.1.4-7","4.1.4-7ubuntu0.1","4.1.4-7ubuntu0.1+esm1","4.1.4-7ubuntu0.1+esm2"]},{"source":"osv","ecosystem":"Ubuntu:Pro:18.04:LTS","package":"zeromq3","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["4.2.1-4ubuntu1","4.2.2-1ubuntu2","4.2.3-1","4.2.3-1build1","4.2.5-1","4.2.5-1ubuntu0.1","4.2.5-1ubuntu0.2","4.2.5-1ubuntu0.2+esm1","4.2.5-1ubuntu0.2+esm2"]},{"source":"osv","ecosystem":"Ubuntu:Pro:20.04:LTS","package":"zeromq3","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["4.3.2-1","4.3.2-2","4.3.2-2ubuntu1","4.3.2-2ubuntu1.20.04.1~esm1","4.3.2-2ubuntu1.20.04.1~esm2"]}],"products":[{"vendor":"fedoraproject","product":"fedora"},{"vendor":"microsoft","product":"zeromq"},{"vendor":"redhat","product":"ceph_storage"},{"vendor":"redhat","product":"enterprise_linux"},{"vendor":"zeromq","product":"zeromq"}],"references":[{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=1921976","tags":["x_refsource_MISC","x_transferred","Issue Tracking","Third Party Advisory","report","web"]},{"url":"https://github.com/zeromq/libzmq/security/advisories/GHSA-qq65-x72m-9wr8","tags":["x_refsource_MISC","x_transferred","Patch","Third Party Advisory","fix","web","report"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-20236"},{"url":"https://github.com/advisories/GHSA-4j25-p3vq-p264"},{"url":"https://docs.bell-sw.com/security/cves/CVE-2021-20236","tags":["advisory"]},{"url":"https://security-tracker.debian.org/tracker/CVE-2021-20236","tags":["advisory"]},{"url":"https://ubuntu.com/security/CVE-2021-20236","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2021-20236","tags":["report"]}],"sources":{"cve":[{"id":"CVE-2021-20236","description":"A flaw was found in the ZeroMQ server in versions before 4.3.3. This flaw allows a malicious client to cause a stack buffer overflow on the server by sending crafted topic subscription requests and then unsubscribing. The highest threat from this vulnerability is to confidentiality, integrity, as well as system availability.","status":"published","published":"2021-05-28T10:42:19Z","modified":"2024-08-03T17:37:23.102Z","cwes":["CWE-120"],"updated_at":"2026-11-02T14:32:55.564736Z"}],"euvd":[{"id":"EUVD-2021-7675","description":"A flaw was found in the ZeroMQ server in versions before 4.3.3. This flaw allows a malicious client to cause a stack buffer overflow on the server by sending crafted topic subscription requests and then unsubscribing. The highest threat from this vulnerability is to confidentiality, integrity, as well as system availability.","status":"published","published":"2021-05-28T10:42:19Z","modified":"2024-08-03T17:37:23Z","updated_at":"2026-11-03T03:25:09.355483Z"}],"ghsa":[{"id":"GHSA-4j25-p3vq-p264","title":"A flaw was found in the ZeroMQ server in versions before 4.3.3. This flaw allows a malicious...","description":"A flaw was found in the ZeroMQ server in versions before 4.3.3. This flaw allows a malicious client to cause a stack buffer overflow on the server by sending crafted topic subscription requests and then unsubscribing. 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The highest threat from this vulnerability is to confidentiality, integrity, as well as system availability.","status":"published","published":"2021-05-28T11:15:07.933Z","modified":"2026-06-17T03:33:31.473Z","cvss":[{"version":"3.1","score":9.8,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"critical","assessor":"primary"},{"version":"2.0","score":7.5,"vector":"AV:N/AC:L/Au:N/C:P/I:P/A:P","level":"high","assessor":"primary"}],"cwes":["CWE-120","CWE-787"],"updated_at":"2026-11-02T14:06:53.987491Z"}],"osv":[{"id":"BELL-CVE-2021-20236","title":"CVE-2021-20236 does not affect BellSoft software","status":"withdrawn","published":"2021-05-28T11:15:00Z","modified":"2026-01-26T09:48:02.442289Z","cvss":[{"version":"3.1","score":9.8,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"critical"}],"updated_at":"2026-11-02T15:28:15.925958Z"},{"id":"CVE-2021-20236","description":"A flaw was found in the ZeroMQ server in versions before 4.3.3. 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The highest threat from this vulnerability is to confidentiality, integrity, as well as system availability.","status":"published","published":"2021-05-28T11:15:07.933Z","modified":"2026-10-23T18:04:48.813382139Z","cvss":[{"version":"3.1","score":9.8,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"critical"}],"updated_at":"2026-11-02T15:45:34.311861Z"},{"id":"JLSEC-2026-516","description":"A flaw was found in the ZeroMQ server in versions before 4.3.3. This flaw allows a malicious client to cause a stack buffer overflow on the server by sending crafted topic subscription requests and then unsubscribing. The highest threat from this vulnerability is to confidentiality, integrity, as well as system availability.","status":"published","published":"2026-05-20T04:02:19.667Z","modified":"2026-07-18T00:00:50.379258408Z","cvss":[{"version":"2.0","score":7.5,"vector":"AV:N/AC:L/Au:N/C:P/I:P/A:P","level":"high"},{"version":"3.1","score":9.8,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"critical"}],"updated_at":"2026-11-02T15:47:18.573531Z"},{"id":"UBUNTU-CVE-2021-20236","description":"A flaw was found in the ZeroMQ server in versions before 4.3.3. This flaw allows a malicious client to cause a stack buffer overflow on the server by sending crafted topic subscription requests and then unsubscribing. 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