CVE-2023-6551Network attack vector

Stored XSS via MIME and extension mismatch

Published Jan 4, 2024 · Updated Jun 3, 2025

Stored XSS in Colin Verot class.upload.php allows remote attackers to execute script in another user's browser through a crafted upload. The default MIME-type allowlist and extension blacklist can accept a polyglot file, such as a valid GIF carrying script under an HTML extension, which process() copies into the destination. Exploitation requires a consuming application to expose uploads and later serve the stored file as active content to a user, enabling script actions within that site's browser context.

CVSS severity5.4
Medium
EPSS probability0.44%
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 Colin Verot class.upload.php allows remote attackers to execute script in another user's browser through a crafted upload. The default MIME-type allowlist and extension blacklist can accept a polyglot file, such as a valid GIF carrying script under an HTML extension, which process() copies into the destination. Exploitation requires a consuming application to expose uploads and later serve the stored file as active content to a user, enabling script actions within that site's browser context.

The record

CVE
CVE-2023-6551
Published
Jan 4, 2024
Updated
Jun 3, 2025
Vendor
Colin Verot
Product
class.upload.php
Classifications
CWE-20, CWE-434, CAPEC-592, CAPEC-209, T1059.007
Attack vector
network
Privileges
Unavailable

Timeline

How it unfolded

  1. Jan 4, 2024CVE publishedPublication date reported by the CVE source.
  2. Jun 3, 2025Record 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=0 <=*

What conditions does exploitation require?

Attack vectornetwork
Required privilegesUnavailable in this record.

What is affected?

Colin Verot · class.upload.phpversion=0 <=*

Published CVSS scores

5.4NISTCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
6.5GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
5.4CISA-ADPCVSS: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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-20Improper Input Validation
CWE-434Unrestricted Upload of File with Dangerous Type
CAPEC-592Stored XSS
CAPEC-209XSS Using MIME Type Mismatch
T1059.007JavaScript/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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