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TI-2026-50093 Aliases CVE-2026-71478GHSA-29pj-957v-52mc

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

Priority MEDIUM 60CWE-692Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
Required
Attack complexity
Low
Impact type
Cross-site scripting
Confidentiality · integrity · availability
Low · Low · None
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-79.

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.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00355 29th percentileScored 2026-11-07
Fix Fixed league/commonmark (Packagist): 2.9.0

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
thephpleaguecommonmark1.5.0 – 2.8.3—No fix listedCNA
—league/commonmark (Packagist)1.5.0 to before 2.9.02.9.0Patch availableGHSA-29pj-957v-52mc
  • commonmark Vendorthephpleague Affected 1.5.0 – 2.8.3 Fixed in — No fix listed CNA
  • league/commonmark (Packagist) Vendor— Affected 1.5.0 to before 2.9.0 Fixed in 2.9.0 Patch available GHSA-29pj-957v-52mc

CPE names Threatist (inferred) · 1

Inferred from how NVD named this product before; not given by a source.

CPEVersionsRoleVendor
cpe:2.3:a:thephpleague:commonmark:*:*:*:*:*:*:*:*——thephpleague
  • cpe:2.3:a:thephpleague:commonmark:*:*:*:*:*:*:*:* Versions — — ·thephpleague

Remediation

  • Fix · GHSA-29pj-957v-52mc league/commonmark (Packagist) Fixed in 2.9.0 Advisory →

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-71478
  2. 2026-10-03 Alias added: GHSA-29pj-957v-52mc

References

Other 4

  • TI-2026-69535 league/commonmark Quadratic DoS via TableStartParser CVSS 4.0HIGH 8.7
  • TI-2026-69534 Cross-site scripting in League CommonMark bypasses DisallowedRawHtml CVSS 4.0MEDIUM 5.3
  • TI-2026-65445 Flysystem: WhitespacePathNormalizer's control-character (CorruptedPathDetected) check is… CVSS 3.1LOW 3.5
  • TI-2021-12376 Time-of-check Time-of-use (TOCTOU) Race Condition in league/flysystem CVSS 3.1CRITICAL 9.8
  • TI-2026-59143 commonmark 1.5.0 before 2.8.4 Denial of Service via Footnote CVSS 4.0HIGH 8.7
  • TI-2026-59142 commonmark 2.0.0 through 2.8.3 Denial of Service via Slug Collision CVSS 4.0HIGH 8.7
See all 20 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences