CVE-2021-23180Public exploit

Code execution or crash via truncated URI delimiter

Published Mar 2, 2022 · Updated Aug 3, 2024

Null-pointer dereference in HTMLDOC before 1.9.12 allows local users to crash the process by converting a crafted HTML file. While writing PDF links, file_extension() copies a URI extension into a fixed buffer, then writes through strchr()'s null return when truncation removes the expected '#' delimiter. Processing attacker-supplied content is required; the public artifact demonstrates a crash, while the CNA also reports arbitrary code execution.

CVSS severity7.8
High
EPSS probability1.35%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Null-pointer dereference in HTMLDOC before 1.9.12 allows local users to crash the process by converting a crafted HTML file. While writing PDF links, file_extension() copies a URI extension into a fixed buffer, then writes through strchr()'s null return when truncation removes the expected '#' delimiter. Processing attacker-supplied content is required; the public artifact demonstrates a crash, while the CNA also reports arbitrary code execution.

The record

CVE
CVE-2021-23180
Published
Mar 2, 2022
Updated
Aug 3, 2024
Vendor
HTMLDOC Project
Product
HTMLDOC
Classifications
CWE-476, T1203
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 2, 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=Fixed in htmldoc v1.9.12 and above.

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

HTMLDOC Project · HTMLDOCversion=Fixed in htmldoc v1.9.12 and above.

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.

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)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-476NULL Pointer Dereference
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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