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Advisory record · GHSA-hh8v-hgvp-g3f5

league/commonmark has an embed extension allowed_domains bypass

CVSS 6.3 MediumEPSS 0.0025 · 16th percentile

Published by the GitHub Advisory Database at 19 Mar 2026, 19:04 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
league/commonmarkPackagist>=2.3.0, <2.8.22.8.2
Identifiers
GHSA-hh8v-hgvp-g3f5 · CVE-2026-33347 · PKSA-21fb-n1x5-5nf7
Weakness (CWE)
CWE-79 · CWE-185 · CWE-918
Tags
Published
19 Mar 2026
Updated
27 Mar 2026

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

The Embed extension's DomainFilteringAdapter in league/commonmark versions 2.3.0 up to 2.8.2 (fixed in 2.8.2) has an allowlist bypass: a domain such as youtube.com.evil passes the check when youtube.com is allowed. An attacker who supplies Markdown to an application using allowed_domains can cause server-side requests to attacker-controlled hosts and inject arbitrary HTML or JavaScript into rendered pages. Upgrade to league/commonmark 2.8.2 or later; as workarounds, disable the Embed extension or restrict it to trusted users.

Written 3 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

ScoreRatingCVSSVectorSource
6.3 Medium 4.0 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 (GitHub_M)
  • CISA KEV Not listed.
  • EPSS 0.0025, the 16th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

  1. 31 Oct 2026, 14:25 UTC First seen by agentprime
  2. 31 Oct 2026, 14:25 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.