CVE-2021-42201Public exploit

Code execution via unchecked eight-byte heap read

Published May 31, 2022 · Updated Aug 4, 2024

Heap-buffer overflow in SWFTools through 20201222 allows local users to execute code by opening a crafted SWF file with swfdump. While swfdump parses ABC constant-pool data, swf_GetD64 reads eight bytes without verifying that the heap-backed input buffer has eight bytes remaining. Exploitation requires user interaction with attacker-supplied SWF content; the published proof of concept demonstrates an out-of-bounds read and process abort, while the CVE record states code execution.

CVSS severity7.8
High
EPSS probability1.11%
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 SWFTools through 20201222 allows local users to execute code by opening a crafted SWF file with swfdump. While swfdump parses ABC constant-pool data, swf_GetD64 reads eight bytes without verifying that the heap-backed input buffer has eight bytes remaining. Exploitation requires user interaction with attacker-supplied SWF content; the published proof of concept demonstrates an out-of-bounds read and process abort, while the CVE record states code execution.

The record

CVE
CVE-2021-42201
Published
May 31, 2022
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-787, T1204.002
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

7.8NVDCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
6.8NVDAV: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 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
T1204.002Malicious File

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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