CVE-2026-33347 PUBLISHED

league/commonmark has an embed extension allowed_domains bypass

Assigner: GitHub_M
Reserved: 18.03.2026 Published: 24.03.2026 Updated: 24.03.2026

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.

Metrics

CVSS 4.0

CVSS Vector: 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
CVSS Score: 6.3

Exploitability Metrics		Vulnerable System Impact Metrics		Subsequent System Impact Metrics
Attack Vector	Network	Confidentiality	None	Confidentiality	Low
Attack Complexity	Low	Integrity	Low	Integrity	Low
Attack Requirements	Present	Availability	None	Availability	None
Privileges Required	None
User Interaction	None

CVSS 4.0

Product Status

Vendor	thephpleague
Product	commonmark
Versions	Version >= 2.3.0, < 2.8.2 is affected

References

Problem Types

CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') CWE
CWE-185: Incorrect Regular Expression CWE
CWE-918: Server-Side Request Forgery (SSRF) CWE