CVE-2021-43529
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 · uneditedThunderbird versions prior to 91.3.0 are vulnerable to the heap overflow described in CVE-2021-43527 when processing S/MIME messages. Thunderbird versions 91.3.0 and later will not call the vulnerable code when processing S/MIME messages that contain certificates with DER-encoded DSA or RSA-PSS signatures.
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 versions before 91.3.0 contain a heap overflow vulnerability (originally identified in CVE-2021-43527) that can be triggered when processing S/MIME messages containing certificates with DER-encoded DSA or RSA-PSS signatures. The vulnerability allows remote code execution through specially crafted S/MIME email messages.
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< 91.3.0CVSS 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.
-
Verify Thunderbird versionOpen Thunderbird and navigate to Help > About Thunderbird, or check the installed package version via system package manager (e.g., dpkg -l | grep thunderbird on Debian-based systems, rpm -qi thunderbird on RHEL-based systems)Affected if Installed version is earlier than 91.3.0
-
Confirm S/MIME is enabledIn Thunderbird, go to Account Settings > End-to-End Encryption and check if S/MIME is enabled for any email accounts. Also check if digital signing is configured under the Security tab for each accountAffected if S/MIME is enabled or configured for digital signing/encryption
-
Check for incoming S/MIME messages with certificatesExamine received S/MIME-signed emails. View message source or use Thunderbird's certificate viewer (View > Message Security) on signed messages to identify if they contain DSA or RSA-PSS signatures in the certificate chainAffected if S/MIME messages with DSA or RSA-PSS signature algorithms in certificates are being processed
Thunderbird is affected only if the installed version is below 91.3.0 AND S/MIME messages containing DER-encoded DSA or RSA-PSS signatures are being processed
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.
dbcve · scoped91.3.0
Upgrade Thunderbird to version 91.3.0 or later. Organizations should verify all installations are updated and consider blocking or flagging S/MIME messages with DSA/PSS signatures until patches are applied.
Thunderbird 91.3.0 or later
- Check current Thunderbird version: Open Thunderbird, go to Help > About Thunderbird
- Download Thunderbird 91.3.0 or later from the official Mozilla website (https://www.thunderbird.net)
- Install the downloaded Thunderbird update
- Restart Thunderbird to complete the update
- Verify the version by checking Help > About Thunderbird shows version 91.3.0 or later
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation1.0 h
- Implementation1.0 h
- Testing2.0 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 $1,376.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-43529 — 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-2021-43529 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
Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.
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