CVE-2026-71478Public exploitNetwork attack vector

Stored XSS via control-byte-obfuscated URL schemes

Published Aug 6, 2026 · Updated Aug 6, 2026

Cross-site scripting in CommonMark 1.5.0 through 2.8.3 allows remote attackers to execute script through crafted Markdown links. AttributesHelper::filterAttributes passes href values whose javascript scheme contains tabs, newlines, or leading C0 controls because its anchored denylist tests the unnormalized string. Exploitation requires an application to enable AttributesExtension, render attacker-controlled Markdown, and present the resulting link to a victim who clicks it.

CVSS severity6.1
Medium
EPSS probability0.25%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in CommonMark 1.5.0 through 2.8.3 allows remote attackers to execute script through crafted Markdown links. AttributesHelper::filterAttributes passes href values whose javascript scheme contains tabs, newlines, or leading C0 controls because its anchored denylist tests the unnormalized string. Exploitation requires an application to enable AttributesExtension, render attacker-controlled Markdown, and present the resulting link to a victim who clicks it.

The record

CVE
CVE-2026-71478
Published
Aug 6, 2026
Updated
Aug 6, 2026
Vendor
The PHP League
Product
CommonMark
Classifications
CWE-692, CWE-79, CWE-86, T1204.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 6, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 6, 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, <= 2.8.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The PHP League · CommonMarkversion=>= 1.5.0, <= 2.8.3

Published CVSS scores

6.1GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A: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-692Incomplete Denylist to Cross-Site Scripting
CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CWE-86Improper Neutralization of Invalid Characters in Identifiers in Web Pages
T1204.001Malicious Link

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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