XSS in Thephpleague Commonmark
CVE-2026-33347
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.
Vulnerability class: XSS (Cross-Site Scripting)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.1 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.
EPSS exploit prediction
EPSS: 0.002 (15.5th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 15th percentile — 15.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: 0.000
Affected products
- Thephpleague Commonmark — versions >= 2.3.0, < 2.8.2
Weakness classification (CWE)
References
- github.com/thephpleague/commonmark/security/advisories/GHSA-hh8v-hgvp-g3f5 (Mitigation, Vendor Advisory)
- github.com/thephpleague/commonmark/commit/59fb075d2101740c337c7216e3f32b36c2042… (Patch)
- github.com/thephpleague/commonmark/releases/tag/2.8.2 (Product, Release Notes)
Frequently asked questions
- What is CVE-2026-33347?
- CVE-2026-33347 is a medium-severity vulnerability in Thephpleague Commonmark, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2026-03-24.
- How severe is CVE-2026-33347?
- Medium severity. CVSS v3 base score is 6.1 out of 10.