CVE-2026-59928Public exploitNetwork attack vector

CPU exhaustion via quadratic reference-definition scans

Published Jul 8, 2026 · Updated Jul 8, 2026

Algorithmic-complexity denial of service in Lepture Mistune before 3.3.0 allows remote attackers to exhaust CPU via crafted Markdown. In block_parser.py, parse_ref_link repeatedly scans forward for the next blank line from each reference definition instead of reusing prior scan results. Any application that passes attacker-supplied Markdown to the default create_markdown() parser can suffer prolonged request processing; no plugins are required.

CVSS severity7.5
High
EPSS probability0.65%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Algorithmic-complexity denial of service in Lepture Mistune before 3.3.0 allows remote attackers to exhaust CPU via crafted Markdown. In block_parser.py, parse_ref_link repeatedly scans forward for the next blank line from each reference definition instead of reusing prior scan results. Any application that passes attacker-supplied Markdown to the default create_markdown() parser can suffer prolonged request processing; no plugins are required.

The record

CVE
CVE-2026-59928
Published
Jul 8, 2026
Updated
Jul 8, 2026
Vendor
Lepture
Product
Mistune
Classifications
CWE-407, CWE-1333, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 8, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 8, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 3.3.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Lepture · Mistuneversion=< 3.3.0

Published CVSS scores

7.5GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-407Inefficient Algorithmic Complexity
CWE-1333Inefficient Regular Expression Complexity
T1499.004Application or System Exploitation

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo