CVE-2026-44897Public exploitNetwork attack vector

Cross-site scripting via unescaped heading IDs

Published May 26, 2026 · Updated May 26, 2026

Cross-site scripting in Mistune before 3.2.1 allows remote attackers to execute JavaScript through crafted Markdown heading text. HTMLRenderer.heading() concatenates a caller-supplied heading_id callback result into an id attribute without escaping, so a double quote adds event-handler attributes. Exploitation requires an application to derive heading IDs from attacker-controlled text and a reader to interact with the rendered heading; the injected script can read same-origin data or alter the page.

CVSS severity6.1
Medium
EPSS probability0.23%
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 Mistune before 3.2.1 allows remote attackers to execute JavaScript through crafted Markdown heading text. HTMLRenderer.heading() concatenates a caller-supplied heading_id callback result into an id attribute without escaping, so a double quote adds event-handler attributes. Exploitation requires an application to derive heading IDs from attacker-controlled text and a reader to interact with the rendered heading; the injected script can read same-origin data or alter the page.

The record

CVE
CVE-2026-44897
Published
May 26, 2026
Updated
May 26, 2026
Vendor
Lepture
Product
Mistune
Classifications
CWE-79, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 26, 2026CVE publishedPublication date reported by the CVE source.
  2. May 26, 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=< 3.2.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Lepture · Mistuneversion=< 3.2.1

Published CVSS scores

6.1GitHub, Inc.CVSS: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.

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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-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1203Exploitation for Client Execution

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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