CVE-2021-42203Public exploit

Code execution via stale heap pointer write

Published May 31, 2022 · Updated Aug 4, 2024

Heap use-after-free in swftools through 20201222 allows local users to execute code by processing a crafted SWF file. swf_ReadTag frees a heap allocation before swf_FontExtract_DefineTextCallback writes two bytes through its stale pointer in swftext.c. Triggering requires a user to run swfdump on attacker-controlled input; the demonstrated result is a process abort, while the CVE record identifies code execution.

CVSS severity7.8
High
EPSS probability1.17%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap use-after-free in swftools through 20201222 allows local users to execute code by processing a crafted SWF file. swf_ReadTag frees a heap allocation before swf_FontExtract_DefineTextCallback writes two bytes through its stale pointer in swftext.c. Triggering requires a user to run swfdump on attacker-controlled input; the demonstrated result is a process abort, while the CVE record identifies code execution.

The record

CVE
CVE-2021-42203
Published
May 31, 2022
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-416, T1203
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 31, 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 vectorlocal
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

6.8NVDAV:N/AC:M/Au:N/C:P/I:P/A:P
7.8NVDCVSS: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-416Use After 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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