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Description

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.

PUBLISHED Reserved 2026-03-18 | Published 2026-03-24 | Updated 2026-03-26 | Assigner GitHub_M




MEDIUM: 6.3CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N

Problem types

CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

CWE-185: Incorrect Regular Expression

CWE-918: Server-Side Request Forgery (SSRF)

Product status

>= 2.3.0, < 2.8.2
affected

References

github.com/...onmark/security/advisories/GHSA-hh8v-hgvp-g3f5

github.com/...ommit/59fb075d2101740c337c7216e3f32b36c204218b

github.com/thephpleague/commonmark/releases/tag/2.8.2

cve.org (CVE-2026-33347)

nvd.nist.gov (CVE-2026-33347)

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