CVE-2021-31554Known exploitationNetwork attack vector

Account-block evasion via nonexistent autocreation target

Published Apr 22, 2021 · Updated Aug 3, 2024

Incorrect authorization in MediaWiki AbuseFilter through 1.35.2 allows remote authenticated users to evade account blocks during autocreation. For autocreateaccount actions, AbuseFilter supplies the not-yet-existing account as both action performer and block target, so target validation leaves the account unblocked. Exploitation requires an existing cross-wiki account to trigger a local account autocreation that matches a block-enabled filter, after which the account can continue activity that the filter intended to stop.

CVSS severity5.4
Medium
EPSS probability0.49%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Incorrect authorization in MediaWiki AbuseFilter through 1.35.2 allows remote authenticated users to evade account blocks during autocreation. For autocreateaccount actions, AbuseFilter supplies the not-yet-existing account as both action performer and block target, so target validation leaves the account unblocked. Exploitation requires an existing cross-wiki account to trigger a local account autocreation that matches a block-enabled filter, after which the account can continue activity that the filter intended to stop.

The record

CVE
CVE-2021-31554
Published
Apr 22, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-863, T1562.001
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

5.4BitnamiCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A: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.

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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 exploitationReported
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-863Incorrect Authorization
T1562.001Impair Defenses: Disable or Modify Tools

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.

Reported exploitation

Technologies

Your stack

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Your stack

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