CVE-2021-42785
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 · uneditedBuffer Overflow vulnerability in tvnviewer.exe of TightVNC Viewer allows a remote attacker to execute arbitrary instructions via a crafted FramebufferUpdate packet from a VNC server.
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 buffer overflow vulnerability exists in tvnviewer.exe (TightVNC Viewer) where improper handling of FramebufferUpdate packets from a malicious VNC server allows overflow of a buffer, leading to arbitrary code execution. The vulnerability is remotely exploitable without authentication.
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<= 2.8.59CVSS 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
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/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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Locate TightVNC Viewer executableSearch for tvnviewer.exe in typical installation directories such as C:\Program Files\TightVNC\ or C:\Program Files (x86)\TightVNC\, or use PowerShell: Get-ChildItem -Path 'C:\Program Files','C:\Program Files (x86)' -Filter 'tvnviewer.exe' -Recurse -ErrorAction SilentlyContinueAffected if tvnviewer.exe is found on the system
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Determine installed TightVNC versionRight-click tvnviewer.exe, select Properties, then view the Details tab for Product Version. Alternatively, query the Windows registry: reg query 'HKLM\SOFTWARE\TightVNC' /v Version or check the uninstall key under HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\UninstallAffected if Version cannot be determined or shows 2.8.59 or lower
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Compare version to affected rangeInterpret the version number found in step 2. Affected versions are 2.8.59 and all prior versions (anything <= 2.8.59)Affected if Installed version is 2.8.59 or any earlier version such as 2.8.8, 2.8.27, etc.
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Verify viewer component presenceConfirm that the tvnviewer.exe file exists and is the TightVNC Viewer component specifically (not the server component tvnserver.exe)Affected if Only the viewer component tvnviewer.exe is present and vulnerable, not just the server
A system is affected if TightVNC Viewer (tvnviewer.exe) version 2.8.59 or lower is installed, as the buffer overflow vulnerability in FramebufferUpdate packet handling applies to the viewer component.
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 dataUpgrade TightVNC Viewer to the latest version with the security fix applied. If no patched version is available, avoid connecting to untrusted or unknown VNC servers, as the attacker only needs to control the VNC server to send a crafted malicious packet.
- Consultation3.0 h
- Implementation6.0 h
- Testing4.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-42785 — 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-2021-42785 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
- No spam, self-promotion, credentials, or personal data