CVE-2021-26259Public exploit

Code execution via unbounded table geometry

Published Mar 3, 2022 · Updated Aug 3, 2024

Heap-buffer overflow in HTMLDOC 1.9.12 allows context-dependent attackers to crash the converter or execute code via crafted HTML. parse_table accepts negative or oversized WIDTH, CELLPADDING, CELLSPACING, and BORDER attributes without bounding the resulting geometry, causing render_table_row to access memory outside a heap allocation. Exploitation requires HTMLDOC to process the crafted document; the demonstrated outcome is a process crash, while the CVE record also identifies arbitrary code execution.

CVSS severity7.8
High
EPSS probability1.21%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap-buffer overflow in HTMLDOC 1.9.12 allows context-dependent attackers to crash the converter or execute code via crafted HTML. parse_table accepts negative or oversized WIDTH, CELLPADDING, CELLSPACING, and BORDER attributes without bounding the resulting geometry, causing render_table_row to access memory outside a heap allocation. Exploitation requires HTMLDOC to process the crafted document; the demonstrated outcome is a process crash, while the CVE record also identifies arbitrary code execution.

The record

CVE
CVE-2021-26259
Published
Mar 3, 2022
Updated
Aug 3, 2024
Vendor
HTMLDOC Project
Product
HTMLDOC
Classifications
CWE-787, T1203
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 3, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=v1.9.12

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

HTMLDOC Project · HTMLDOCversion=v1.9.12

Published CVSS scores

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

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)
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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