{"id":"CVE-2021-33500","aliases":["EUVD-2021-20201","GHSA-vmq2-m9cv-qwqx","UBUNTU-CVE-2021-33500"],"status":"published","title":"PuTTY before 0.75 on Windows allows remote servers to cause a denial of service (Windows GUI hang...","description":"PuTTY before 0.75 on Windows allows remote servers to cause a denial of service (Windows GUI hang) by telling the PuTTY window to change its title repeatedly at high speed, which results in many SetWindowTextA or SetWindowTextW calls. NOTE: the same attack methodology may affect some OS-level GUIs on Linux or other platforms for similar reasons.","severity":{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AC:L/AV:N/A:H/C:N/I:N/PR:N/S:U/UI:N","level":"high","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-11","score":0.01914,"percentile":0.80104,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":false},"published":"2021-05-21T19:42:26Z","modified":"2026-10-17T12:56:20Z","affected":[{"source":"osv","ecosystem":"Ubuntu:16.04:LTS","package":"putty","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.65-2","0.66-1","0.66-2","0.66-3","0.66-4","0.67-1","0.67-2","0.67-3build0.16.04.1","0.67-3+deb9u1build0.16.04.1"]},{"source":"osv","ecosystem":"Ubuntu:18.04:LTS","package":"putty","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.70-1","0.70-2","0.70-3","0.70-4"]},{"source":"osv","ecosystem":"Ubuntu:20.04:LTS","package":"putty","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.72-1","0.73-1","0.73-2"]},{"source":"osv","ecosystem":"Ubuntu:22.04:LTS","package":"putty","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.75-3","0.76-1","0.76-2"]},{"source":"osv","ecosystem":"Ubuntu:24.04:LTS","package":"putty","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.78-3","0.79-1","0.80-1","0.80-1build2","0.80-1build3","0.81-1"]},{"source":"osv","ecosystem":"Ubuntu:25.10","package":"putty","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.83-2","0.83-3"]},{"source":"osv","ecosystem":"Ubuntu:26.10","package":"putty","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.83-3build1","0.84-1"]},{"source":"osv","ecosystem":"Ubuntu:26.04:LTS","package":"putty","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.83-3","0.83-3build1"]}],"products":[{"vendor":"putty","product":"putty"}],"references":[{"url":"https://www.chiark.greenend.org.uk/~sgtatham/putty/changes.html","tags":["x_refsource_MISC","x_transferred","Release Notes","Third Party Advisory","report"]},{"url":"https://docs.ssh-mitm.at/puttydos.html","tags":["x_refsource_MISC","x_transferred","Exploit","Third Party Advisory","report"]},{"url":"https://github.com/ssh-mitm/ssh-mitm-plugins/blob/main/ssh_mitm_plugins/ssh/putty_dos.py","tags":["x_refsource_MISC","x_transferred","Exploit","Third Party Advisory","report"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-33500"},{"url":"https://github.com/advisories/GHSA-vmq2-m9cv-qwqx"},{"url":"https://ubuntu.com/security/CVE-2021-33500","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2021-33500","tags":["report"]}],"sources":{"cve":[{"id":"CVE-2021-33500","description":"PuTTY before 0.75 on Windows allows remote servers to cause a denial of service (Windows GUI hang) by telling the PuTTY window to change its title repeatedly at high speed, which results in many SetWindowTextA or SetWindowTextW calls. NOTE: the same attack methodology may affect some OS-level GUIs on Linux or other platforms for similar reasons.","status":"published","published":"2021-05-21T19:42:26Z","modified":"2024-08-03T23:50:42.977Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AC:L/AV:N/A:H/C:N/I:N/PR:N/S:U/UI:N","level":"high","assessor":"cna"}],"updated_at":"2026-11-02T14:33:10.204494Z"}],"euvd":[{"id":"EUVD-2021-20201","description":"PuTTY before 0.75 on Windows allows remote servers to cause a denial of service (Windows GUI hang) by telling the PuTTY window to change its title repeatedly at high speed, which results in many SetWindowTextA or SetWindowTextW calls. NOTE: the same attack methodology may affect some OS-level GUIs on Linux or other platforms for similar reasons.","status":"published","published":"2021-05-21T19:42:26Z","modified":"2024-08-03T23:50:42Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AC:L/AV:N/A:H/C:N/I:N/PR:N/S:U/UI:N","level":"high"}],"updated_at":"2026-11-03T03:24:34.304953Z"}],"ghsa":[{"id":"GHSA-vmq2-m9cv-qwqx","title":"PuTTY before 0.75 on Windows allows remote servers to cause a denial of service (Windows GUI hang...","description":"PuTTY before 0.75 on Windows allows remote servers to cause a denial of service (Windows GUI hang) by telling the PuTTY window to change its title repeatedly at high speed, which results in many SetWindowTextA or SetWindowTextW calls. NOTE: the same attack methodology may affect some OS-level GUIs on Linux or other platforms for similar reasons.","status":"published","published":"2022-05-24T19:02:54Z","modified":"2023-01-29T05:06:18Z","updated_at":"2026-11-02T14:45:59.496932Z"}],"nvd":[{"id":"CVE-2021-33500","description":"PuTTY before 0.75 on Windows allows remote servers to cause a denial of service (Windows GUI hang) by telling the PuTTY window to change its title repeatedly at high speed, which results in many SetWindowTextA or SetWindowTextW calls. NOTE: the same attack methodology may affect some OS-level GUIs on Linux or other platforms for similar reasons.","status":"published","published":"2021-05-21T20:15:07.723Z","modified":"2026-06-17T03:54:41.047Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high","assessor":"secondary"},{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high","assessor":"primary"},{"version":"2.0","score":5,"vector":"AV:N/AC:L/Au:N/C:N/I:N/A:P","level":"medium","assessor":"primary"}],"updated_at":"2026-11-02T14:06:53.987491Z"}],"osv":[{"id":"UBUNTU-CVE-2021-33500","description":"PuTTY before 0.75 on Windows allows remote servers to cause a denial of service (Windows GUI hang) by telling the PuTTY window to change its title repeatedly at high speed, which results in many SetWindowTextA or SetWindowTextW calls. 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