CVE-2021-33500: Putty

High severity, CVSS 7.5. EPSS: 1.9% chance of exploitation in the next 30 days.

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.

Affected products

• Putty Putty: before 0.75 (fixed in 0.75)

Published 2021-05-21. Last modified 2026-06-17.