Is CVE-2021-43529 actively exploited?

No active exploitation of CVE-2021-43529 has been confirmed so far. Continue monitoring, as exploit status can change.

Can CVE-2021-43529 be exploited remotely?

Yes. CVE-2021-43529 is exploitable remotely over the network (CVSS attack vector: Network).

What is the CVSS score of CVE-2021-43529?

CVE-2021-43529 has a CVSS score of 9.8 (CRITICAL).

HOME VULNERABILITIESCVE-2021-43529

CRITICAL

CVE-2021-43529

CWE-787Published: February 16, 2023· Updated: Jun 17, 2026

9.8

CVSS v3.1

Official Description

Thunderbird 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.

NVD Source

Risk Analysis

Thunderbird versions prior to 91.3.0 are vulnerable to a heap overflow when processing specific S/MIME messages. This critical flaw allows for remote code execution, resulting in a 9.8 CVSS score.

There is no public exploit known for this issue, and it is not included in the CISA KEV. It is considered remotely exploitable.

Recommended Action

Update Thunderbird to version 91.3.0 or later to ensure the vulnerable code path is no longer executed.

Generated by the CTIWATCH analysis pipeline from this CVE's metadata (CVSS, EPSS, KEV status, exploit intelligence). Verify against vendor advisories before acting.

Technical Analysis

CVE-2021-43529 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in complete confidentiality breach (data exposure), full integrity compromise (data manipulation), availability disruption (denial of service), with a CVSS base score of 9.8.

From a weakness classification perspective (CWE-787): Out-of-bounds write vulnerabilities can lead to data corruption, crashes, or arbitrary code execution.