CVE-2021-23158Public exploitNetwork attack vector

Arbitrary code execution via double-free

Published Mar 16, 2022 · Updated Aug 3, 2024

Double-free in HTMLDOC 1.9.12 and earlier allows attackers to execute arbitrary code or crash the converter via crafted HTML input. The pspdf_export function frees the same htmlGetText-allocated buffer twice while exporting a malformed document, producing a write-what-where condition. Exploitation requires the target to convert attacker-controlled HTML; successful heap corruption can terminate the process or alter execution.

CVSS severity9.8
Critical
EPSS probability2.44%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Double-free in HTMLDOC 1.9.12 and earlier allows attackers to execute arbitrary code or crash the converter via crafted HTML input. The pspdf_export function frees the same htmlGetText-allocated buffer twice while exporting a malformed document, producing a write-what-where condition. Exploitation requires the target to convert attacker-controlled HTML; successful heap corruption can terminate the process or alter execution.

The record

CVE
CVE-2021-23158
Published
Mar 16, 2022
Updated
Aug 3, 2024
Vendor
HTMLDOC Project
Product
HTMLDOC
Classifications
CWE-415, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 16, 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

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=Affects v1.9.12 and before.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

HTMLDOC Project · HTMLDOCversion=Affects v1.9.12 and before.

Published CVSS scores

9.8NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.5NVDAV:N/AC:L/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.

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-415Double Free
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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