CVE-2026-49851

What it is

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.

At a glance

Exploitability

Can be exploited over the network without logging in. High risk of service disruption.

Exploit odds

0.5% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-06-24 18:17 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-10-25 22:10 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.5% in the next 30 days (EPSS).
• Severity: 8.7 HIGH (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2026-06-24 18:17 UTC

Last modified

2026-10-25 22:10 UTC

Exploit probability

0.5% · EPSS, next 30 days

Weakness

CWE-400 · Uncontrolled resource consumption

Record status

Deferred

Attack profile CVSS 4.0 · 8.7

Attack vector

Network

Complexity

Low

Attack requirements

None

Privileges needed

None

User interaction

None

Confidentiality

None

Integrity

None

Availability

High

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2026-49851.md and follow it. Check whether this project is affected by CVE-2026-49851. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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