CVE-2021-26235
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 · uneditedFastStone Image Viewer <= 7.5 is affected by a user mode write access violation near NULL at 0x005bdfc9, triggered when a user opens or views a malformed CUR file that is mishandled by FSViewer.exe. Attackers could exploit this issue for a Denial of Service (DoS) or possibly to achieve code execution.
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 · high confidenceFastStone Image Viewer <= 7.5 contains a user-mode write access violation vulnerability when parsing malformed CUR (Windows cursor) files. The software writes to an invalid memory location near NULL (0x005bdfc9) due to insufficient bounds checking or validation during CUR file parsing in FSViewer.exe, allowing attackers to cause a denial of service or potentially achieve code execution.
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 data<= 7.5CVSS 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
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/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 FastStone Image Viewer versionOpen FastStone Image Viewer, go to Help > About, or right-click FSViewer.exe and select Properties > Details to view the version numberAffected if The displayed version is 7.5 or any version lower than 7.5
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Locate the FSViewer.exe executableSearch for FSViewer.exe in the program installation directory (commonly C:\Program Files\FastStone Image Viewer or C:\Program Files (x86)\FastStone Image Viewer)Affected if FSViewer.exe exists and is the executable handling CUR file parsing
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Verify the file version of FSViewer.exeRight-click FSViewer.exe > Properties > Details > File Version to confirm the exact build numberAffected if File version shows 7.5 or lower, confirming the vulnerable executable is in use
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Check if CUR file association is configuredLook for .cur file associations in Windows: go to Control Panel > Default Programs > Set Associations, or attempt to open a CUR file with FastStone Image Viewer to see if the software is registered to handle such filesAffected if FastStone Image Viewer is set as the default or available handler for .cur files, making the vulnerable parsing code reachable
If FastStone Image Viewer version is 7.5 or lower and FSViewer.exe processes CUR files, the environment is affected by this vulnerability.
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 dataAvoid opening untrusted or malformed CUR files with FastStone Image Viewer until a patched version is available. Upgrade to a version newer than 7.5 when released.
- Consultation3.0 h
- Implementation8.0 h
- Testing4.0 h
- Review / QA2.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2021-26235 — 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-2021-26235 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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- 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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