CVE-2021-40833
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedA vulnerability affecting F-Secure antivirus engine was discovered whereby unpacking UPX file can lead to denial-of-service. The vulnerability can be exploited remotely by an attacker. A successful attack will result in denial-of-service of the antivirus engine.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · moderate confidenceA denial-of-service vulnerability exists in F-Secure's antivirus scanning engine when processing UPX-packed files. The vulnerability is triggered during the UPX unpacking routine, where a specially crafted malicious file can cause the antivirus engine to crash or become unresponsive, resulting in denial of service.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE dataall versionsall versionsall versionsall versionsall versionsCVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Local
- Complexity
- Low
- Privileges
- None
- User interaction
- Required
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify installed F-Secure productRun system package manager or check installed software list to determine which F-Secure product from the affected list is installed (Atlant, Internet Gatekeeper, Linux Security, Linux Security 64, or Elements Endpoint Protection)Affected if Any of the five listed products is installed and has not been updated beyond the vulnerable version
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Check antivirus engine versionUse the F-Secure command-line tool (fsdiag or equivalent) or check the engine version through the product interface to retrieve the current scanning engine version numberAffected if The engine version is older than the patched version released by F-Secure for this CVE
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Check virus definition dateInspect the antivirus definition/pattern file date through the product status or fsav --version commandAffected if The definition files predate the security update released for CVE-2021-40833
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Verify UPX scanning is enabledExamine the antivirus real-time or on-demand scanning configuration to confirm that UPX-packed file decompression/scanning is not explicitly disabled or excludedAffected if UPX scanning is active and the engine/definitions are unpatched
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Test UPX file processing capabilityIf safe to do so in a test environment, scan a benign UPX-packed file using the installed F-Secure product and observe for crashes or hangs during the unpacking routineAffected if The engine crashes, hangs, or becomes unresponsive when processing a UPX-packed file
A user is affected if they have any of the listed F-Secure products installed with engine/definition versions predating the CVE-2021-40840833 security update and UPX scanning is enabled.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataOrganizations should apply F-Secure's security updates or patches for this vulnerability. Ensure antivirus definitions and engine versions are updated to the latest vendor release.
- Consultation2.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,800.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-40833 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-40833 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.
- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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