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.

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-match…

Vulnerability class: XSS (Cross-Site Scripting)

EPSS: 0.002 (15.3th percentile) — read the EPSS interpretation.

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.

Affected products

Thephpleague Commonmark — versions >= 2.3.0, < 2.8.2

Weakness classification (CWE)

References

security-advisories@github.com (x_refsource_CONFIRM, Mitigation, Vendor Advisory)
security-advisories@github.com (Patch, x_refsource_MISC)
security-advisories@github.com (Product, x_refsource_MISC, 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.