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Fencer Vulns
medium 6.1

CVE-2026-33347 json

league/commonmark has an embed extension allowed_domains bypass

published 2026-03-19 7 mo ago modified 2026-06-17 4 mo ago also EUVD-2026-20079 , GHSA-hh8v-hgvp-g3f5

cvss
6.1
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 16%
public exploits
0
none known

Summary

league/commonmark is a PHP Markdown parser. From version 2.3.0 to before version 2.8.2, the DomainFilteringAdapter in the Embed extension is vulnerable to an allowlist bypass due to a missing hostname boundary assertion in the domain-matching regex. An attacker-controlled domain like youtube.com.evil passes the allowlist check when youtube.com is an allowed domain. This issue has been patched in version 2.8.2.

Patch / fix

  • packagist league/commonmark 2.8.2
  • thephpleague commonmark 2.8.2
  • php-league-commonmark Debian 12 2.3.9-1+deb12u1
  • php-league-commonmark Debian 13 2.7.0-1+deb13u1
  • php-league-commonmark Debian 14 2.8.2-1

debian advisories DEBIAN-CVE-2026-33347

  • php-league-commonmark Ubuntu Pro 20.04 LTS 1.3.1-1ubuntu2+esm1
  • php-league-commonmark Ubuntu Pro 22.04 LTS 1.6.7-1ubuntu0.1~esm1
  • php-league-commonmark Ubuntu Pro 24.04 LTS 2.4.2-2ubuntu0.1~esm1

ubuntu advisories UBUNTU-CVE-2026-33347

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
7 mo ago

Exploit prediction

0.25% chance of exploitation in the next 30 days, higher than 16% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 4.0 6.3 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N
CNA 4.0 6.3 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
NVD 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
>=2.3.0, <2.8.2
2.8.2

Affected products

  • thephpleague commonmark

Classification

Weakness
  • CWE-79 Improper Neutralization of Input During Web Page Generation
  • CWE-185 Incorrect Regular Expression
  • CWE-918 Server-Side Request Forgery

References

Sources

Fencer Vulns 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.