CVE-2021-42040Public exploitNetwork attack vector

Service hang via unenforced parser loop limit

Published Oct 6, 2021 · Updated Aug 4, 2024

Denial of service in the MediaWiki Loops extension through 1.36.2 allows remote attackers to hang PHP-FPM with crafted page content. The loop-control parser code fails to enforce egLoopsCountLimit, so a #while expression with a true condition continues indefinitely. Exploitation requires the Loops extension and permission to submit parser markup; the runaway request consumes PHP-FPM resources and interrupts wiki service.

CVSS severity7.5
High
EPSS probability1.16%
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 the MediaWiki Loops extension through 1.36.2 allows remote attackers to hang PHP-FPM with crafted page content. The loop-control parser code fails to enforce egLoopsCountLimit, so a #while expression with a true condition continues indefinitely. Exploitation requires the Loops extension and permission to submit parser markup; the runaway request consumes PHP-FPM resources and interrupts wiki service.

The record

CVE
CVE-2021-42040
Published
Oct 6, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-835, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 6, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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

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

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

CWE-835Loop with Unreachable Exit Condition ('Infinite Loop')
T1499.004Endpoint Denial of Service: Application or System Exploitation

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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