CVE-2021-33500
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.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (1.91%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
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.
- CVSS 3.1
- 7.5 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- EPSS
- 1.91% probability · 80th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Affected
- putty/putty
- Source
- cve@mitre.org
EPSS 1.9% since 26 October 2026; no change recorded yet. Points are recorded when the score first appears and whenever it moves by a percentage point or more.
References
- https://docs.ssh-mitm.at/puttydos.htmlExploit, Third Party Advisory
- https://github.com/ssh-mitm/ssh-mitm-plugins/blob/main/ssh_mitm_plugins/ssh/putty_dos.pyExploit, Third Party Advisory
- https://www.chiark.greenend.org.uk/~sgtatham/putty/changes.htmlRelease Notes, Third Party Advisory
- https://docs.ssh-mitm.at/puttydos.htmlExploit, Third Party Advisory
- https://github.com/ssh-mitm/ssh-mitm-plugins/blob/main/ssh_mitm_plugins/ssh/putty_dos.pyExploit, Third Party Advisory
- https://www.chiark.greenend.org.uk/~sgtatham/putty/changes.htmlRelease Notes, Third Party Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.