CVE-2021-33500

Name: CVE-2021-33500
Creator: NVD / NIST
Published: 2021-05-21T20:15:07.723+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 7.5/10EPSS 1.97%

Last modified Jun 17, 2026

CVE-2021-33500 is a high-severity vulnerability rated 7.5/10 on the CVSS scale. 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.. EPSS estimates a 1.97% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS Probability

1.97%

77.9th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Vendor	Product	Versions
Putty	Putty	< 0.75

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

Timeline

Published: May 21, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-33500?

How severe is CVE-2021-33500?

CVE-2021-33500 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 1.97% probability of exploitation in the next 30 days.

How do I fix CVE-2021-33500?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-33500?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST