league/commonmark is a PHP Markdown parser. A cross-site scripting (XSS) vulnerability in the Attributes extension of the league/commonmark library (versions 1.5.0 through 2.6.x) allows remote attackers to insert malicious JavaScript calls into HTML. The league/commonmark library provides configuration options such as `html_input: 'strip'` and `allow_unsafe_links: false` to mitigate cross-site scripting (XSS) attacks by stripping raw HTML and disallowing unsafe links. However, when the Attributes Extension is enabled, it introduces a way for users to inject arbitrary HTML attributes into elements via Markdown syntax using curly braces. Version 2.7.0 contains three changes to prevent this XSS attack vector: All attributes starting with `on` are considered unsafe and blocked by default; support for an explicit allowlist of allowed HTML attributes; and manually-added `href` and `src` attributes now respect the existing `allow_unsafe_links` configuration option. If upgrading is not feasible, please consider disabling the `AttributesExtension` for untrusted users and/or filtering the rendered HTML through a library like HTMLPurifier.

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. A cross-site scripting (XSS) vulnerability in the Attributes     extension of the league/commonmark library (versions 1.5.0 through 2.6.x) allows remote attackers to     insert malicious JavaScript calls into HTML. The league/commonmark library provides configuration options     such as `html_input: 'strip'` and `allow_unsafe_links: false` to mitigate cross-site scripting (XSS)     attacks by stripping raw HTML and disallowing unsafe links. However, when the Attributes Extension is     enabled, it introduces a way for users to inject arbitrary HTML attributes into elements via Markdown     syntax using curly braces. Version 2.7.0 contains three changes to prevent this XSS attack vector: All     attributes starting with `on` are considered unsafe and blocked by default; support for an explicit     allowlist of allowed HTML attributes; and manually-added `href` and `src` attributes now respect the     existing `allow_unsafe_links` configuration option. If upgrading is not feasible, please consider     disabling the `AttributesExtension` for untrusted users and/or filtering the rendered HTML through a     library like HTMLPurifier. (CVE-2025-46734)

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. A cross-site scripting (XSS) vulnerability in the Attributes
    extension of the league/commonmark library (versions 1.5.0 through 2.6.x) allows remote attackers to
    insert malicious JavaScript calls into HTML. The league/commonmark library provides configuration options
    such as `html_input: 'strip'` and `allow_unsafe_links: false` to mitigate cross-site scripting (XSS)
    attacks by stripping raw HTML and disallowing unsafe links. However, when the Attributes Extension is
    enabled, it introduces a way for users to inject arbitrary HTML attributes into elements via Markdown
    syntax using curly braces. Version 2.7.0 contains three changes to prevent this XSS attack vector: All
    attributes starting with `on` are considered unsafe and blocked by default; support for an explicit
    allowlist of allowed HTML attributes; and manually-added `href` and `src` attributes now respect the
    existing `allow_unsafe_links` configuration option. If upgrading is not feasible, please consider
    disabling the `AttributesExtension` for untrusted users and/or filtering the rendered HTML through a
    library like HTMLPurifier. (CVE-2025-46734)

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
255893	Linux Distros Unpatched Vulnerability : CVE-2025-46734	Nessus	Misc.	Local	medium
434712	SCA: security update for league/commonmark (GHSA-3527-qv2q-pfvx)	Tenable Cloud Security	SCA Checks	Local	medium
434712	SCA: security update for league/commonmark (GHSA-3527-qv2q-pfvx)	Tenable Self-Hosted Container Security	SCA Checks	Local	medium

Detections

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CVE-2025-46734

medium

Tenable Plugins

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medium

medium

medium