CVE-2021-33500Public exploitNetwork attack vector

Windows GUI hang via unthrottled title updates

Published May 21, 2021 · Updated Aug 3, 2024

Denial of service in PuTTY terminal-title handling before 0.75 on Windows allows remote attackers controlling a server to hang the GUI. PuTTY passes rapid server-controlled title updates to SetWindowTextA or SetWindowTextW without rate limiting, overwhelming the Windows interface. The client must connect to an attacker-controlled server, or a server-side application must be able to write to its terminal; the reported consequence is an unresponsive Windows desktop.

CVSS severity7.5
High
EPSS probability1.97%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in PuTTY terminal-title handling before 0.75 on Windows allows remote attackers controlling a server to hang the GUI. PuTTY passes rapid server-controlled title updates to SetWindowTextA or SetWindowTextW without rate limiting, overwhelming the Windows interface. The client must connect to an attacker-controlled server, or a server-side application must be able to write to its terminal; the reported consequence is an unresponsive Windows desktop.

The record

CVE
CVE-2021-33500
Published
May 21, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 21, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

5.0NVDAV:N/AC:L/Au:N/C:N/I:N/A:P
7.5MITRECVSS:3.1/AC:L/AV:N/A:H/C:N/I:N/PR:N/S:U/UI:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

T1499Endpoint Denial of Service

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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