CVE-2021-43579Public exploit

Code execution via signed BMP color count

Published Nov 12, 2021 · Updated Aug 4, 2024

Stack-based buffer overflow in HTMLDOC 1.9.13 and earlier allows attackers to execute code when a crafted BMP-linked HTML file is converted. image_load_bmp() casts the BMP header's colors_used value to a signed integer, lets a large value become negative and bypass the 256-entry limit, then passes it to fread() as the count for a fixed 256-by-4-byte stack colormap. Execution requires the victim to convert an HTML document that links to the crafted BMP, and successful exploitation runs code with the HTMLDOC process's privileges.

CVSS severity7.8
High
EPSS probability7.35%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stack-based buffer overflow in HTMLDOC 1.9.13 and earlier allows attackers to execute code when a crafted BMP-linked HTML file is converted. image_load_bmp() casts the BMP header's colors_used value to a signed integer, lets a large value become negative and bypass the 256-entry limit, then passes it to fread() as the count for a fixed 256-by-4-byte stack colormap. Execution requires the victim to convert an HTML document that links to the crafted BMP, and successful exploitation runs code with the HTMLDOC process's privileges.

The record

CVE
CVE-2021-43579
Published
Nov 12, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-787, T1203
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 12, 2021CVE 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 vectorlocal
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
6.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A: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.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-787Out-of-bounds Write
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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