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VulnerabilityPublished

CVE-2026-71478: thephpleague commonmark · Cross-site Scripting

Affects thephpleague commonmarkSource CVE Database V5

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Not known to be exploited · CVSS 6.1 Medium : upgrade to 2.9.0 when convenient.

Data as of 5 Nov 2026, 00:01 UTC

CVSS 3.1 base score
6.1Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.3% chance of exploitation in 30 days – higher than 29% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 2.9.0
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 6 Aug 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 5 Nov 2026.

What to do

Upgrade thephpleague/commonmark to 2.9.0.

Affected software

ProductAffectedFixed in
thephpleaguecommonmarkAffected
  • >=1.5.0 <=2.8.3
Fixed in–
Packagistthephpleague/commonmarkpkg:composer/thephpleague/commonmarkOther threatsAffected
  • <2.9.0 >=1.5.0
Fixed in
  • 2.9.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Upgrade to version 2.9.0 or later of the league/commonmark library, where this vulnerability is fixed. No other official remediation or temporary fixes are documented. Patch status is confirmed by the version fix information.

Description

league/commonmark is a PHP library for parsing and rendering CommonMark Markdown. From 1.5.0 until 2.9.0, the AttributesExtension's href and src unsafe-link filter can be bypassed by embedding control bytes, such as a tab, carriage return, line feed, or leading C0 control character, in a javascript: URL that browsers discard before parsing the scheme, causing the browser to still execute the script even when the unsafe-link filter is enabled. This issue is fixed in 2.9.0.

References

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