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Debian LinuxOperating system · Debian

CVE-2021-38502

MEDIUM · 5.9 CVSS v3.1 Published 2021-11-03
Fix available
A fix is available. Upgrade to 91.2 or later.
See remediation →
68/100
Remediation priority · Elevated
Remotely reachable No privileges Zero-click

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 · unedited
Thunderbird ignored the configuration to require STARTTLS security for an SMTP connection. A MITM could perform a downgrade attack to intercept transmitted messages, or could take control of the authenticated session to execute SMTP commands chosen by the MITM. If an unprotected authentication method was configured, the MITM could obtain the authentication credentials, too. This vulnerability affects Thunderbird < 91.2.

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 confidence

Thunderbird failed to enforce STARTTLS security for SMTP connections even when configured to require it, allowing MITM attackers to perform downgrade attacks, intercept messages, hijack authenticated sessions, and potentially capture authentication credentials if unprotected auth methods were used.

MitigationUpdate Thunderbird to version 91.2 or later to remediate this vulnerability.

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
Debian LinuxOperating system
Affected:= 9.0= 10.0= 11.0
ThunderbirdApplication
Affected:< 91.2

CVSS 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
High
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

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 checks

Work through these to decide whether this CVE applies to you.

  1. Check if Thunderbird is installed
    Run `dpkg -l | grep -i thunderbird` on Debian systems, or check for the Thunderbird application in the system package manager.
    Affected if Thunderbird is not found in the package list, meaning the system is not affected by this client-side vulnerability.
  2. Determine installed Thunderbird version
    Run `dpkg -l | grep -i thunderbird` and examine the version number in the output, or open Thunderbird and go to Help > About Thunderbird to view the version.
    Affected if The displayed version number is lower than 91.2 (e.g., 91.1, 78.x, etc.).
  3. Verify SMTP account configuration (if Thunderbird is installed)
    Open Thunderbird, go to Account Settings > Outgoing Server (SMTP), select the configured SMTP server, and examine the security settings. Check if 'STARTTLS' or 'SSL/TLS' is selected in the connection security dropdown.
    Affected if The SMTP server is configured to use STARTTLS or SSL/TLS and the Thunderbird version is below 91.2, making the downgrade attack possible.

A system is affected if Thunderbird is installed with a version lower than 91.2 and is configured to use SMTP with STARTTLS or TLS encryption, as the vulnerability allows MITM attackers to strip the STARTTLS requirement.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 · scoped
Upgrade available Upgrade to 91.2 or later
Fixed in 91.2
Interim mitigation

Update Thunderbird to version 91.2 or later to remediate this vulnerability.

Recommended fix High confidence

Thunderbird 91.2 or later

  1. Check current Thunderbird version (Help > About Thunderbird)
  2. Update Thunderbird to version 91.2 or later via the application's automatic update feature
  3. On Debian systems, also run: sudo apt update && sudo apt upgrade thunderbird
  4. Verify the update was successful by checking the version again
  5. For manual download, visit https://www.thunderbird.net/ and download version 91.2 or newer
Caveat Security update with minimal risk; verify any custom SMTP server configurations after upgrading

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Debian Linux Scoped from the published advisory
  • Consultation1.0 h
  • Implementation2.0 h
  • Testing1.0 h
  • Review / QA1.0 h
5.0 hours of engineering $890
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-38502 in production — separate from our analysis above.

No notes yet

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What this is

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.

What belongs here
  • 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