dbcve.org
Debian LinuxOperating system · Debian

CVE-2021-43528

MEDIUM · 6.5 CVSS v3.1 Published 2021-12-08
Fix available
A fix is available. Upgrade to 91.4.0 or later.
See remediation →
72/100
Remediation priority · Elevated
Remotely reachable No privileges

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 unexpectedly enabled JavaScript in the composition area. The JavaScript execution context was limited to this area and did not receive chrome-level privileges, but could be used as a stepping stone to further an attack with other vulnerabilities. This vulnerability affects Thunderbird < 91.4.0.

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

JavaScript was unexpectedly enabled in Thunderbird's email composition area, creating an unintended execution context. While the sandbox did not provide chrome-level privileges, this vulnerability could be exploited as an attack vector to chain with other flaws for more severe impact.

MitigationUpgrade Thunderbird to version 91.4.0 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:< 91.4.0

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
Low
Privileges
None
User interaction
Required
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/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. Verify Thunderbird is installed
    Run 'which thunderbird' or check package manager: 'dpkg -l | grep thunderbird' (Debian) or 'rpm -qa | grep thunderbird' (RPM-based)
    Affected if Thunderbird is not installed on the system
  2. Determine installed Thunderbird version
    Run 'thunderbird --version' from command line, or open Thunderbird and go to Help > About Thunderbird
    Affected if Unable to determine version or Thunderbird responds to version query
  3. Compare version against affected range
    Compare the installed version number to 91.4.0 - versions below 91.4.0 are affected (e.g., 91.3.0, 91.2.0, 78.x, etc.)
    Affected if Installed version is less than 91.4.0 (for example, 91.3.2 or any 78.x release)
  4. Check Debian package version if using system package
    Run 'dpkg -l thunderbird' to see the installed Debian package version
    Affected if Package version is less than 1:91.4.0-1 (or similar 91.4.x version for your distribution)

A system is affected if Thunderbird (either direct install or via Debian package) is present at a version lower than 91.4.0, as those versions contain the unexpected JavaScript execution context in the email composition area.

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 91.4.0 or later
Fixed in 91.4.0
Interim mitigation

Upgrade Thunderbird to version 91.4.0 or later to remediate this vulnerability.

Recommended fix High confidence

Thunderbird 91.4.0 or later

  1. Update your system's package repository to ensure you have the latest package lists
  2. Upgrade Thunderbird to version 91.4.0 or later using your system's package manager (e.g., apt-get update && apt-get install thunderbird for Debian)
  3. Verify the installed Thunderbird version matches or exceeds 91.4.0 (e.g., thunderbird --version)
  4. Restart Thunderbird if it was running during the upgrade
  5. If using Debian, ensure you have the latest security updates from Debian's security repository (deb.debian.org)
Caveat Minimal risk - this is a security fix; however, test basic email functionality after upgrade to ensure normal operation

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
  • Implementation1.0 h
  • Testing2.0 h
  • Review / QA1.0 h
5.0 hours of engineering $860
Get the upgrade done

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

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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-2021-43528 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