What’s Vulnerable › Vulnerabilities

CVE-2026-33347: league/commonmark has an embed extension allowed_domains bypass

• Severity: medium (CVSS 6.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-03-24 · updated 2026-06-17
• Weakness: CWE-79

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.

Affected products

• thephpleague commonmark: from 2.3.0 before 2.8.2 — fixed in 2.8.2

How to fix

Upgrade to a fixed version: thephpleague commonmark 2.8.2. Check the vendor advisory for mitigations.

References

• https://github.com/thephpleague/commonmark/commit/59fb075d2101740c337c7216e3f32b36c204218b
• https://github.com/thephpleague/commonmark/releases/tag/2.8.2
• https://github.com/thephpleague/commonmark/security/advisories/GHSA-hh8v-hgvp-g3f5

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