CVE-2023-37255Public exploitNetwork attack vector

Stored XSS via unescaped User-Agent rendering

Published Jun 29, 2023 · Updated Nov 26, 2024

Stored XSS in Wikimedia Foundation CheckUser through 1.39.3 allows remote attackers to execute script via a crafted User-Agent header. Special:CheckUser's get-edits result renders the stored user-agent value without first escaping it for HTML output. The payload executes only when a privileged CheckUser operator inspects an associated edit or logged action, limiting the consequence to that operator's browser session.

CVSS severity6.1
Medium
EPSS probability0.47%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stored XSS in Wikimedia Foundation CheckUser through 1.39.3 allows remote attackers to execute script via a crafted User-Agent header. Special:CheckUser's get-edits result renders the stored user-agent value without first escaping it for HTML output. The payload executes only when a privileged CheckUser operator inspects an associated edit or logged action, limiting the consequence to that operator's browser session.

The record

CVE
CVE-2023-37255
Published
Jun 29, 2023
Updated
Nov 26, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-79, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 29, 2023CVE publishedPublication date reported by the CVE source.
  2. Nov 26, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

6.1NIST NVDCVSS: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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