CVE-2026-53962Network attack vector

Stored XSS via retained SVG DTD entities

Published Jul 9, 2026 · Updated Jul 9, 2026

Stored cross-site scripting in Discourse before 2026.6.0 allows remote authenticated users to execute script through a crafted SVG. The clean_svg! upload sanitizer leaves internal DTD entity references intact, allowing an SVG entity to expand into script when served through upload or avatar URLs. Low-privilege upload access and a victim visiting a specific, nonroutine URL are required; the script executes in the forum's browser origin despite CSP.

CVSS severity5.4
Medium
EPSS probability0.41%
Next 30 days · Sep 17, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stored cross-site scripting in Discourse before 2026.6.0 allows remote authenticated users to execute script through a crafted SVG. The clean_svg! upload sanitizer leaves internal DTD entity references intact, allowing an SVG entity to expand into script when served through upload or avatar URLs. Low-privilege upload access and a victim visiting a specific, nonroutine URL are required; the script executes in the forum's browser origin despite CSP.

The record

CVE
CVE-2026-53962
Published
Jul 9, 2026
Updated
Jul 9, 2026
Vendor
Discourse
Product
Discourse
Classifications
CWE-79, T1059.007
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jul 9, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 9, 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=>= 2026.1.0-latest, < 2026.1.5
  2. Affected versionversion=>= 2026.4.0-latest, < 2026.4.2
  3. Affected versionversion=>= 2026.5.0-latest, < 2026.5.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Discourse · Discourseversion=>= 2026.1.0-latest, < 2026.1.5; version=>= 2026.4.0-latest, < 2026.4.2; version=>= 2026.5.0-latest, < 2026.5.1

Published CVSS scores

5.4GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/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 11, 2026Sep 17, 2026
Latest reporting daySep 17, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1059.007Command and Scripting Interpreter: JavaScript/JScript

Public exploit references

No public exploit references are available in this record.

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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