CVE-2021-39593Public exploit

Local crash via NULL font-info dereference

Published Sep 20, 2021 · Updated Aug 4, 2024

NULL pointer dereference in SWFTools through 20200710 allows local users to crash swfdump by processing a crafted SWF file. The swf_FontExtract_DefineFontInfo() routine in modules/swftext.c fails while extracting DefineFontInfo data, but public sources do not identify the pointer that becomes NULL or the malformed field that triggers it. Execution requires a user to process the file locally; the demonstrated consequence is termination of the swfdump process, with no reported confidentiality or integrity impact.

CVSS severity5.5
Medium
EPSS probability0.66%
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 SWFTools through 20200710 allows local users to crash swfdump by processing a crafted SWF file. The swf_FontExtract_DefineFontInfo() routine in modules/swftext.c fails while extracting DefineFontInfo data, but public sources do not identify the pointer that becomes NULL or the malformed field that triggers it. Execution requires a user to process the file locally; the demonstrated consequence is termination of the swfdump process, with no reported confidentiality or integrity impact.

The record

CVE
CVE-2021-39593
Published
Sep 20, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-476, T1204.002
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 20, 2021CVE 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

5.5NVDCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
5.5CanonicalCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
4.3NVDAV:N/AC:M/Au:N/C:N/I:N/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 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
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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