CVE-2021-29949
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 · uneditedWhen loading the shared library that provides the OTR protocol implementation, Thunderbird will initially attempt to open it using a filename that isn't distributed by Thunderbird. If a computer has already been infected with a malicious library of the alternative filename, and the malicious library has been copied to a directory that is contained in the search path for executable libraries, then Thunderbird will load the incorrect library. This vulnerability affects Thunderbird < 78.9.1.
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 confidenceThunderbird attempts to load an OTR protocol shared library using a filename that differs from the one distributed with the application. If a malicious library with that alternative filename already exists in a directory within the system's executable library search path, Thunderbird will load and execute the malicious code instead of the legitimate library. This is a classic library search order hijacking vulnerability requiring pre-existing system compromise.
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< 78.9.1CVSS 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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Verify Thunderbird installationCheck if Thunderbird is installed on the system. On Linux, use 'which thunderbird' or check /usr/bin/thunderbird. On Windows, check Program Files for Mozilla Thunderbird folder or look in the registry.Affected if Thunderbird is not installed on the system.
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Determine installed Thunderbird versionRun Thunderbird with version flag: 'thunderbird --version' on Linux, or check the application properties in Windows. On macOS, right-click Thunderbird in Applications and select Get Info.Affected if The version displayed cannot be determined or retrieved.
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Compare version against affected rangeCompare the installed version number to the affected range: versions prior to 78.9.1 are vulnerable. Note that version 78.9.1 and later are patched.Affected if The installed Thunderbird version is less than 78.9.1 (for example, 78.9.0, 78.8.x, 78.7.x, or any earlier major version).
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Identify OTR library loading behaviorThis vulnerability stems from Thunderbird loading an OTR protocol library with a different filename than distributed. If your system is already compromised with a malicious library in a system library path, exploitation could occur. Review system library search paths (echo $LD_LIBRARY_PATH on Linux, check PATH on Windows).Affected if Untrusted directories exist in system library search paths AND Thunderbird version is below 78.9.1.
A user is affected if their installed Thunderbird version is lower than 78.9.1 AND an attacker has already placed a malicious library with the alternate filename in a directory within the system's executable library search path.
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 data78.9.1
Upgrade Thunderbird to version 78.9.1 or later. Additionally, ensure systems are not already compromised and that only trusted, secure directories are included in the system library search path.
- Consultation1.0 h
- Implementation2.0 h
- Testing1.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-29949 — 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-2021-29949 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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- Version or environment caveats, and links to real fixes
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