CVE-2021-40833Network attack vector

Antivirus engine denial of service via UPX unpacking

Published Nov 26, 2021 · Updated Aug 4, 2024

Denial of service in the F-Secure antivirus engine allows remote attackers to interrupt malware scanning with a crafted UPX file. The UPX unpacking path fails while processing attacker-controlled packed content, but F-Secure has not disclosed the precise resource-management error. The crafted file must reach an affected product's scanning path; successful exploitation stops the antivirus engine and interrupts malware scanning.

CVSS severity5.5
Medium
EPSS probability0.39%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in the F-Secure antivirus engine allows remote attackers to interrupt malware scanning with a crafted UPX file. The UPX unpacking path fails while processing attacker-controlled packed content, but F-Secure has not disclosed the precise resource-management error. The crafted file must reach an affected product's scanning path; successful exploitation stops the antivirus engine and interrupts malware scanning.

The record

CVE
CVE-2021-40833
Published
Nov 26, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-404, T1499
Attack vector
network
Privileges
Unavailable

Timeline

How it unfolded

  1. Nov 26, 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 vectornetwork
Required privilegesUnavailable in this record.

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:N/A:P
5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
5.5F-SecureCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:L

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
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-404Improper Resource Shutdown or Release
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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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