CVE-2026-86429Public exploitNetwork attack vector

Service interruption via quadratic extension parsing

Published Sep 7, 2026 · Updated Sep 7, 2026

Quadratic parsing in The PHP League CommonMark 1.5.0 through 2.9.0 allows remote attackers to interrupt service with crafted Markdown. SmartPunct repeatedly recopies a growing text node for unpaired quotes, while Attributes repeatedly scans sibling runs and rebuilds accumulated class lists. Exposure requires an embedding application to register either non-default extension and process attacker-controlled Markdown; exploitation consumes CPU and can occupy PHP workers without disclosing or altering data.

CVSS severity8.7
High
EPSS probability0.29%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Quadratic parsing in The PHP League CommonMark 1.5.0 through 2.9.0 allows remote attackers to interrupt service with crafted Markdown. SmartPunct repeatedly recopies a growing text node for unpaired quotes, while Attributes repeatedly scans sibling runs and rebuilds accumulated class lists. Exposure requires an embedding application to register either non-default extension and process attacker-controlled Markdown; exploitation consumes CPU and can occupy PHP workers without disclosing or altering data.

The record

CVE
CVE-2026-86429
Published
Sep 7, 2026
Updated
Sep 7, 2026
Vendor
The PHP League
Product
CommonMark
Classifications
CWE-407, CWE-1050, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 7, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 7, 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=1.5.0 <2.9.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The PHP League · CommonMarkversion=1.5.0 <2.9.1

Published CVSS scores

7.5GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
7.5VulnCheck CNACVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
8.7VulnCheck CNACVSS: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.

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

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-407Inefficient Algorithmic Complexity
CWE-1050Excessive Platform Resource Consumption within a Loop
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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