Vulnerability record · CVE-2021-33500 · published 21 May 2021

CVE-2021-33500: Putty vulnerability

Putty · Putty

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.

7.5 CVSS 3.1 High EPSS 2.0% · top 20.4%

7.5CVSS 3.1 base score, v2 5.0

2.0%EPSS exploitation probability, 30 days

NoNot in CISA KEV

1Affected product versions listed by NVD

6References, 4 tagged exploit

17 Jun 2026Last modified by NVD

Description

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

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

Putty Putty

References

Link	Tags
https://docs.ssh-mitm.at/puttydos.html	ExploitThird Party Advisory
https://github.com/ssh-mitm/ssh-mitm-plugins/blob/main/ssh_mitm_plugins/ssh/putty_dos.py	ExploitThird Party Advisory
https://www.chiark.greenend.org.uk/~sgtatham/putty/changes.html	Release NotesThird Party Advisory
https://docs.ssh-mitm.at/puttydos.html	ExploitThird Party Advisory
https://github.com/ssh-mitm/ssh-mitm-plugins/blob/main/ssh_mitm_plugins/ssh/putty_dos.py	ExploitThird Party Advisory
https://www.chiark.greenend.org.uk/~sgtatham/putty/changes.html	Release NotesThird Party Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

10.0CVE-2004-1008Putty vulnerabilityInteger signedness error in the ssh2_rdpkt function in PuTTY before 0.56 allows remote attackers to execute arbitrary code via a SSH2_MSG_DEBUG packe…EPSS 7.4%10 Jan 2005 10.0CVE-2002-1357Cisco ios memory buffer overflow vulnerabilityMultiple SSH2 servers and clients do not properly handle packets or data elements with incorrect length specifiers, which may allow remote attackers …EPSS 9.8%23 Dec 2002 10.0CVE-2002-1358Cisco ios improper input validation vulnerabilityMultiple SSH2 servers and clients do not properly handle lists with empty elements or strings, which may allow remote attackers to cause a denial of …EPSS 5.8%23 Dec 2002 10.0CVE-2002-1359SSH2 implementations mishandle large packets, enabling DoS and possible code executionMultiple SSH2 servers and clients fail to properly handle large packets or large fields, leading to buffer overflow conditions. The flaw was demonstr…EPSS 80%analysed23 Dec 2002 10.0CVE-2002-1360Cisco ios improper input validation vulnerabilityMultiple SSH2 servers and clients do not properly handle strings with null characters in them when the string length is specified by a length field, …EPSS 6.1%23 Dec 2002 9.8CVE-2019-17067Putty allocation without limits vulnerabilityPuTTY before 0.73 on Windows improperly opens port-forwarding listening sockets, which allows attackers to listen on the same port to steal an incomi…EPSS 1.6%1 Oct 2019 9.8CVE-2019-9895Putty memory buffer overflow vulnerabilityIn PuTTY versions before 0.71 on Unix, a remotely triggerable buffer overflow exists in any kind of server-to-client forwarding.EPSS 2.6%21 Mar 2019 9.8CVE-2019-9898Putty vulnerabilityPotential recycling of random numbers used in cryptography exists within PuTTY before 0.71.EPSS 3.9%21 Mar 2019

Source: NIST National Vulnerability Database (record CVE-2021-33500), CISA KEV, FIRST EPSS (scores of 2026-09-29). This page is refreshed as NVD updates the record.