CVE-2021-31553Network attack vector

CheckUserLog denial of service via untrimmed usernames

Published Apr 22, 2021 · Updated Aug 3, 2024

Denial of service in MediaWiki CheckUser through 1.35.2 allows remote authenticated users to disable CheckUserLog via a trailing-space username. CheckUser stores the untrimmed target in cu_log, and LogPager later processes the malformed cul_target_text; the fixes trim both values. CheckUser privileges are required, and exploitation prevents access to CheckUserLog and disrupts usage tracking without stopping the wiki.

CVSS severity6.5
Medium
EPSS probability1.40%
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 MediaWiki CheckUser through 1.35.2 allows remote authenticated users to disable CheckUserLog via a trailing-space username. CheckUser stores the untrimmed target in cu_log, and LogPager later processes the malformed cul_target_text; the fixes trim both values. CheckUser privileges are required, and exploitation prevents access to CheckUserLog and disrupts usage tracking without stopping the wiki.

The record

CVE
CVE-2021-31553
Published
Apr 22, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-428, T1499.004
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Apr 22, 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 privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
6.4NIST NVDAV:N/AC:L/Au:N/C:N/I:P/A:P

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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-428Unquoted Search Path or Element
T1499.004Application or System Exploitation Flaws

Public exploit references

No public exploit references are available in this record.

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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