CVE-2024-56156Public exploitNetwork attack vector

Stored XSS via polyglot extension mismatch

Published Apr 25, 2025 · Updated Feb 3, 2026

Stored cross-site scripting in Halo before 2.20.13 allows remote attackers to execute script via uploaded polyglot files. LocalAttachmentUploadHandler validates detected content type and size but does not compare the filename extension, so a BMP/HTML/JAR polyglot named .html passes as image/bmp. The uploaded file must be opened by a victim; script then runs with that user's privileges, and an administrator session permits plugin installation and code execution.

CVSS severity9.0
Critical
EPSS probability0.76%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stored cross-site scripting in Halo before 2.20.13 allows remote attackers to execute script via uploaded polyglot files. LocalAttachmentUploadHandler validates detected content type and size but does not compare the filename extension, so a BMP/HTML/JAR polyglot named .html passes as image/bmp. The uploaded file must be opened by a victim; script then runs with that user's privileges, and an administrator session permits plugin installation and code execution.

The record

CVE
CVE-2024-56156
Published
Apr 25, 2025
Updated
Feb 3, 2026
Vendor
Halo
Product
Halo
Classifications
CWE-79, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 25, 2025CVE publishedPublication date reported by the CVE source.
  2. Feb 3, 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=< 2.20.13

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Halo · Haloversion=< 2.20.13

Published CVSS scores

9.0NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H
5.5GitHub, Inc.CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:L/E:P

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-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1190Exploit Public-Facing Application

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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