CVE-2021-43659Public exploitNetwork attack vector

Stored XSS via unrestricted avatar file extensions

Published Mar 24, 2022 · Updated Aug 4, 2024

Stored XSS in Halo 1.4.14's avatar upload feature allows remote authenticated users to execute script when a victim opens an uploaded HTML file. The uploader accepts arbitrary filename extensions, stores HTML as an avatar asset, and serves it so browsers parse embedded script. An authenticated upload and victim interaction are required; the demonstrated script reads Halo access-token and user data from local storage.

CVSS severity5.4
Medium
EPSS probability0.55%
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 Halo 1.4.14's avatar upload feature allows remote authenticated users to execute script when a victim opens an uploaded HTML file. The uploader accepts arbitrary filename extensions, stores HTML as an avatar asset, and serves it so browsers parse embedded script. An authenticated upload and victim interaction are required; the demonstrated script reads Halo access-token and user data from local storage.

The record

CVE
CVE-2021-43659
Published
Mar 24, 2022
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-79, T1539
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 24, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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 privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

3.5NVDAV:N/AC:M/Au:S/C:N/I:P/A:N
5.4NVDCVSS: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.

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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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1539Steal Web Session Cookie

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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