CVE-2021-43529

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.

Published: 2023-02-16 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-43529 is rated Moderate Risk (52.2/100): CVSS Critical severity, with low exploitation likelihood (EPSS 0.47%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-43529

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.33% 0.47% +0.14%
2 2026-02-24 0.09% 0.33% +0.24%
3 2025-11-21 — 0.09% —

Full EPSS history (8 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-43529

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
9.8 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 5.9 [email protected]
9.8 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 5.9 134c704f-9b21-4f2e-91b3-4a467353bcc0

Weakness enumeration for CVE-2021-43529

OS Trackers for CVE-2021-43529

vendor priority summary link
alpine — CVE-2021-43529: 1 source package rows (thunderbird); 20 state rows across 2 repos (3.22-community, edge-community); fixed 0, open 20. https://security.alpinelinux.org/vuln/CVE-2021-43529
debian not yet assigned CVE-2021-43529 not yet assigned priority: Debian including 1 source packages (thunderbird), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2021-43529
gentoo high CVE-2021-43529: 1 GLSA(s) (202208-14), 2 atom(s) (mail-client/thunderbird, mail-client/thunderbird-bin); latest impact high. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-43529
redhat critical — https://access.redhat.com/security/cve/CVE-2021-43529
suse high CVE-2021-43529 severity important: SUSE including 1 source package names (thunderbird-91.3.0-2.el8_4), 1 product×package rows across 1 product lines (SUSE Liberty Linux 8): Fixed 1. https://www.suse.com/security/cve/CVE-2021-43529/
ubuntu medium CVE-2021-43529 medium priority: Ubuntu including 1 source packages (thunderbird), 10 status rows across 10 suites (bionic, focal, hirsute, impish, jammy, kinetic, lunar, trusty, upstream, xenial): not-affected 4, ignored 3, released 3. https://ubuntu.com/security/CVE-2021-43529

Affected software / configurations for CVE-2021-43529

Vendor Product Version Raw CPE
mozilla thunderbird < 91.3.0 cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*

References for CVE-2021-43529

cvelogic Threat Intelligence