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Fencer Intel
medium 6.1

CVE-2026-71478 json

league/commonmark: AttributesExtension href/src unsafe-link filter bypass via embedded control bytes

published 3mo ago modified 18d ago also EUVD-2026-54261 , GHSA-29pj-957v-52mc

cvss
6.1
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 29%
public exploits
0
none known

Summary

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.

Patch / fix

  • packagist league/commonmark 2.9.0
  • thephpleague commonmark 2.9.0
  • php-league-commonmark Debian 14 2.9.0-1

debian advisories DEBIAN-CVE-2026-71478

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CISA SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
partial
Assessed
3mo ago

Exploit prediction

0.36% chance of exploitation in the next 30 days, higher than 29% of all scored CVEs (FIRST EPSS, 2026-11-11).

Exploits and checks

  • github.com https://github.com/thephpleague/commonmark/security/advisories/GHSA-29pj-957v-52mc referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
GitHub 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Affected packages

ecosystem package affected fixed in
packagist league/commonmark
>=1.5.0, <2.9.0
2.9.0

Affected products

  • thephpleague commonmark

Classification

Weakness
  • CWE-79 Improper Neutralization of Input During Web Page Generation
  • CWE-86 Improper Neutralization of Invalid Characters in Identifiers in Web Pages
  • CWE-692 Incomplete Denylist to Cross-Site Scripting

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.