CVE-2021-40836Network attack vector

Antivirus engine denial of service via PST scanning

Published Dec 22, 2021 · Updated Aug 4, 2024

Denial of service in the F-Secure antivirus engine allows remote attackers to interrupt scanning by supplying a crafted Outlook PST file. F-Secure has not disclosed the parser operation or malformed PST structure that causes the engine to fail during file inspection. Exploitation requires the engine to scan the file, after which antivirus protection is interrupted; no code execution is reported.

CVSS severity4.6
Medium
EPSS probability0.46%
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 scanning by supplying a crafted Outlook PST file. F-Secure has not disclosed the parser operation or malformed PST structure that causes the engine to fail during file inspection. Exploitation requires the engine to scan the file, after which antivirus protection is interrupted; no code execution is reported.

The record

CVE
CVE-2021-40836
Published
Dec 22, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
T1499
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Dec 22, 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 privilegesauthenticated

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
4.3NVDAV:N/AC:M/Au:N/C:N/I:N/A:P
4.6F-SecureCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:N/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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

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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