CVE-2026-49851Public exploitNetwork attack vector

CPU exhaustion via quadratic link-text scanning

Published Jun 24, 2026 · Updated Jun 24, 2026

Algorithmic-complexity DoS in Mistune before 3.3.0 allows remote attackers to exhaust CPU via crafted Markdown input. In mistune/inline_parser.py, parse_link_text searches to the end for a closing bracket on each failed link parse, while the outer loop advances one character, producing quadratic work for repeated opening brackets. The condition is reachable only when a consuming application passes attacker-controlled Markdown to Mistune; the bounded consequence is CPU saturation that delays or blocks parsing.

CVSS severity8.7
High
EPSS probability0.63%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Algorithmic-complexity DoS in Mistune before 3.3.0 allows remote attackers to exhaust CPU via crafted Markdown input. In mistune/inline_parser.py, parse_link_text searches to the end for a closing bracket on each failed link parse, while the outer loop advances one character, producing quadratic work for repeated opening brackets. The condition is reachable only when a consuming application passes attacker-controlled Markdown to Mistune; the bounded consequence is CPU saturation that delays or blocks parsing.

The record

CVE
CVE-2026-49851
Published
Jun 24, 2026
Updated
Jun 24, 2026
Vendor
Lepture
Product
Mistune
Classifications
CWE-770, CWE-407, CWE-400, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 24, 2026CVE publishedPublication date reported by the CVE source.
  2. Jun 24, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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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

8.7GitHub, Inc.CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

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.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
CWE-407Inefficient Algorithmic Complexity
CWE-400Uncontrolled Resource Consumption
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

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Your stack

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