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.

The remote Ubuntu 20.04 LTS / 22.04 LTS / 24.04 LTS host has a package installed that is affected by multiple vulnerabilities as referenced in the USN-8194-1 advisory.

    It was discovered that league/commonmark did not properly restrict unsafe attributes when the Attributes     extension was enabled. An attacker could possibly use this issue to cause cross-site scripting by     injecting malicious code into rendered HTML. This issue only affected Ubuntu 22.04 LTS and Ubuntu 24.04     LTS. (CVE-2025-46734)

    It was discovered that league/commonmark did not properly block certain disallowed HTML tags in some     cases. An attacker could possibly use this issue to cause cross-site scripting by inserting malicious HTML     that bypassed filtering. (CVE-2026-30838)

    It was discovered that league/commonmark did not properly enforce domain allowlist checks in the Embed     extension. An attacker could possibly use this issue to bypass domain restrictions and cause untrusted     content to be treated as allowed. This issue only affected Ubuntu 24.04 LTS. (CVE-2026-33347)

Tenable has extracted the preceding description block directly from the Ubuntu security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - 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. (CVE-2026-33347)

Note that Nessus relies on the presence of the package as reported by the vendor.

There are packages installed that are affected by a vulnerability referenced in the following CVE:

  - 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. (CVE-2026-33347)

ID	Name	Product	Family	Type	Severity
309186	Ubuntu 20.04 LTS / 22.04 LTS / 24.04 LTS : league/commonmark vulnerabilities (USN-8194-1)	Nessus	Ubuntu Local Security Checks	Local	medium
303380	Linux Distros Unpatched Vulnerability : CVE-2026-33347	Nessus	Misc.	Local	medium
439041	SCA: security update for league/commonmark (GHSA-hh8v-hgvp-g3f5)	Tenable Cloud Security	SCA Checks	Local	medium
439041	SCA: security update for league/commonmark (GHSA-hh8v-hgvp-g3f5)	Tenable Self-Hosted Container Security	SCA Checks	Local	medium

Detections

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CVE-2026-33347

medium

Tenable Plugins

medium

medium

medium

medium