Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, Mistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n²)) behavior in parse_link_text. When parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior. An attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload. This vulnerability is fixed in 3.3.0.

An update of the python3 package has been released.

The remote openSUSE 16 host has a package installed that is affected by a vulnerability as referenced in the openSUSE- SU-2026:21191-1 advisory.

    This update for python-mistune fixes the following issue

    - CVE-2026-49851: potential DoS via quadratic-time parsing in parse_link_text (bsc#1269091).

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

Note that Nessus has not tested for this issue 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, Mistune is vulnerable to a     CPU exhaustion DoS due to superlinear (approximately O(n)) behavior in parse_link_text. When parsing     Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a     regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in     quadratic-time behavior. An attacker-controlled Markdown input can therefore trigger excessive CPU usage     with a very small payload. This vulnerability is fixed in 3.3.0. (CVE-2026-49851)

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

ID	Name	Product	Family	Type	Severity
332604	Photon OS 5.0: Python3 PHSA-2026-5.0-91-0911	Nessus	PhotonOS Local Security Checks	Local	high
332506	Photon OS 5.0: Python3 PHSA-2026-5.0-92-0911	Nessus	PhotonOS Local Security Checks	Local	high
325050	openSUSE 16 Security Update : python-mistune (openSUSE-SU-2026:21191-1)	Nessus	SuSE Local Security Checks	Local	high
324560	Photon OS 5.0: Python3 PHSA-2026-5.0-0911	Nessus	PhotonOS Local Security Checks	Local	high
322674	Linux Distros Unpatched Vulnerability : CVE-2026-49851	Nessus	Misc.	Local	high

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