Medium severity · published Mar 24, 2026
CVE-2026-33347
league/commonmark has an embed extension allowed_domains bypass
6.1
CVSS
0.2%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Confidentiality
Low
Integrity
Low
Availability
None
Scope
Changed
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 16% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
CO
commonmark · thephpleague
>= 2.3.0, < 2.8.2 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-33347
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-33347
Patch
https://github.com/thephpleague/commonmark/commit/59fb075d2101740c337c7216e3f32b36c204218b
Product
https://github.com/thephpleague/commonmark/releases/tag/2.8.2
Mitigation
https://github.com/thephpleague/commonmark/security/advisories/GHSA-hh8v-hgvp-g3f5
More from commonmark
7.5
CVE-2026-105830
league/commonmark 2.0.0 before 2.10.2 Quadratic DoS via TableStartParser
7.5
CVE-2024-58382
league/commonmark before 2.6.0 Denial of Service via Quadratic Complexity
7.5
CVE-2026-86435
commonmark 1.5.0 before 2.8.4 Denial of Service via Footnote
7.5
CVE-2026-86434
commonmark 2.0.0 through 2.8.3 Denial of Service via Slug Collision
7.5
CVE-2026-86433
commonmark 1.5.0 before 2.8.4 Denial of Service via Attributes