Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the safe_url filter in src/mistune/renderers/html.py blocks only javascript:, vbscript:, file:, and data: schemes, allowing legacy or chained schemes such as feed:, view-source:, jar:, livescript:, mocha:, ms-its:, mk:, and res: to reach rendered href and src attributes and potentially execute script in affected user agents. This issue is fixed in version 3.3.0.

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

  - Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the safe_url filter in
    src/mistune/renderers/html.py blocks only javascript:, vbscript:, file:, and data: schemes, allowing
    legacy or chained schemes such as feed:, view-source:, jar:, livescript:, mocha:, ms-its:, mk:, and res:
    to reach rendered href and src attributes and potentially execute script in affected user agents. This
    issue is fixed in version 3.3.0. (CVE-2026-59929)

An update of the python3 package has been released.

The remote SUSE Linux SLES16 / SLES_SAP16 host has a package installed that is affected by multiple vulnerabilities as referenced in the SUSE-SU-2026:22655-1 advisory.

    This update for python-mistune fixes the following issues

    - CVE-2026-59922: quadratic-time parsing on long runs of some markers in `formatting.py` can lead to DoS     (bsc#1271117).
    - CVE-2026-59923: `HTMLRenderer.safe_url()` does not block percent-encoded javascript URIs and allows for     XSS       (bsc#1271119).
    - CVE-2026-59924: improper processing of user-supplied include paths in `Include.parse()` can lead to path     traversal       and arbitrary file reads (bsc#1271121).
    - CVE-2026-59925: quadratic-time parsing on long runs of some emphasis pairs in `inline_parser` can lead     to DoS       (bsc#1271125).
    - CVE-2026-59926: improper escaping in `render_admonition()` can lead to atribute injection and XSS     (bsc#1271127).
    - CVE-2026-59927: uncontrolled recursion when processing two markdown files that include each other can     lead to a DoS        (bsc#1271128).
    - CVE-2026-59928: quadratic-time parsing on long lists of repeated reference-link definitions in     `block_parser` can       lead to DoS (bsc#1271131).
    - CVE-2026-59929: HARMFUL_PROTOCOLS list misses legacy and chained schemes and allow arbitrary script     execution in       user agents (bsc#1271132).
    - CVE-2026-59930: the `toc` plugin and `TableOfContents` directive generate heading IDs with predictable     values and       allow for collisions with attacker-controlled `id=toc_N` content (bsc#1271082).

Tenable has extracted the preceding description block directly from the SUSE 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 remote openSUSE 16 host has a package installed that is affected by multiple vulnerabilities as referenced in the openSUSE-SU-2026:21339-1 advisory.

    This update for python-mistune fixes the following issues

    - CVE-2026-59922: quadratic-time parsing on long runs of some markers in `formatting.py` can lead to DoS     (bsc#1271117).
    - CVE-2026-59923: `HTMLRenderer.safe_url()` does not block percent-encoded javascript URIs and allows for     XSS       (bsc#1271119).
    - CVE-2026-59924: improper processing of user-supplied include paths in `Include.parse()` can lead to path     traversal       and arbitrary file reads (bsc#1271121).
    - CVE-2026-59925: quadratic-time parsing on long runs of some emphasis pairs in `inline_parser` can lead     to DoS       (bsc#1271125).
    - CVE-2026-59926: improper escaping in `render_admonition()` can lead to atribute injection and XSS     (bsc#1271127).
    - CVE-2026-59927: uncontrolled recursion when processing two markdown files that include each other can     lead to a DoS        (bsc#1271128).
    - CVE-2026-59928: quadratic-time parsing on long lists of repeated reference-link definitions in     `block_parser` can       lead to DoS (bsc#1271131).
    - CVE-2026-59929: HARMFUL_PROTOCOLS list misses legacy and chained schemes and allow arbitrary script     execution in       user agents (bsc#1271132).
    - CVE-2026-59930: the `toc` plugin and `TableOfContents` directive generate heading IDs with predictable     values and       allow for collisions with attacker-controlled `id=toc_N` content (bsc#1271082).

Tenable has extracted the preceding description block directly from the SUSE 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.

  - Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the safe_url filter in     src/mistune/renderers/html.py blocks only javascript:, vbscript:, file:, and data: schemes, allowing     legacy or chained schemes such as feed:, view-source:, jar:, livescript:, mocha:, ms-its:, mk:, and res:
    to reach rendered href and src attributes and potentially execute script in affected user agents. This     issue is fixed in version 3.3.0. (CVE-2026-59929)

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

ID	Name	Product	Family	Type	Severity
465339	Echo: mistune: security update to 3.3.0	Tenable Cloud Security	Echo Local Security Checks	Local	medium
465339	Echo: mistune: security update to 3.3.0	Tenable Self-Hosted Container Security	Echo Local Security Checks	Local	medium
334706	Photon OS 5.0: Python3 PHSA-2026-5.0-92-0947	Nessus	PhotonOS Local Security Checks	Local	medium
327587	SUSE SLES16 Security Update : python-mistune (SUSE-SU-2026:22655-1)	Nessus	SuSE Local Security Checks	Local	medium
327239	openSUSE 16 Security Update : python-mistune (openSUSE-SU-2026:21339-1)	Nessus	SuSE Local Security Checks	Local	medium
325839	Linux Distros Unpatched Vulnerability : CVE-2026-59929	Nessus	Misc.	Local	medium

Detections

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CVE-2026-59929

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Tenable Plugins

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medium