Inefficient Algorithmic Complexity Vulnerability in Mistune by Lepture
CVE-2026-115347

8.7HIGH

Key Information:

Vendor

Lepture

Status
Mistune
Vendor
CVE Published:
22 October 2026

What is CVE-2026-115347?

Mistune, a popular Markdown parsing library, is prone to a denial of service attack due to an inefficient algorithmic complexity flaw in its parse_link_text function. This vulnerability allows remote attackers to exploit the library by crafting markdown with long sequences of unmatched square brackets. When processed by mistune.html(), these sequences initiate repeated forward scans, causing significant delays and potentially stalling worker processes for extended periods. As a result, this can lead to service disruptions for applications relying on this library.

Affected Version(s)

mistune 0 < 3.3.0

mistune 3.3.0

References

https://github.com/lepture/mistune/security/advisories/GH...
vendor-advisory
https://www.vulncheck.com/advisories/mistune-before-3.3.0...
third-party-advisory

CVSS V4

Score:
8.7
Severity:
HIGH
Confidentiality:
None
Integrity:
None
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
None
Privileges Required:
Undefined
User Interaction:
None

Timeline

  • Vulnerability published

  • Vulnerability Reserved

.