CVE-2021-40529

Exp

The ElGamal implementation in Botan through 2.18.1, as used in Thunderbird and other products, allows plaintext recovery because, during interaction between two cryptographic libraries, a certain dangerous combination of the prime defined by the receiver's public key, the generator defined by the receiver's public key, and the sender's ephemeral exponents can lead to a cross-configuration attack against OpenPGP.

Published: 2021-09-06 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-40529 is rated Exploit Available (56.4/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 0.28%). 1 public exploit reference(s) are indexed (Exploit-DB). Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

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

Public exploit references (Exploit-DB) for CVE-2021-40529

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2021-40529

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 2025-11-21 0.37% 0.28% -0.09%
2 2025-11-18 0.28% 0.37% +0.09%
3 2025-08-16 — 0.28% —

Full EPSS history (17 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-40529

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.9 3.1 MEDIUM
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N 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:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
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:N)
Data isn’t meaningfully altered or forged.
Availability (A:N)
Service keeps running; no real outage angle.
 2.2 3.6 [email protected]
2.6 2.0 LOW
AV:N/AC:H/Au:N/C:P/I:N/A:N Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:H)
Exploitation requires uncommon or highly specific conditions.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:N)
No availability impact.
 4.9 2.9 [email protected]

Weakness enumeration for CVE-2021-40529

OS Trackers for CVE-2021-40529

vendor priority summary link
alpine medium CVE-2021-40529: 1 source package rows (botan); 29 state rows across 8 repos (3.11-main, 3.12-main, 3.17-main, 3.18-main, 3.19-main, 3.20-main, 3.21-main, edge-main); fixed 7, open 22. https://security.alpinelinux.org/vuln/CVE-2021-40529
debian not yet assigned CVE-2021-40529 not yet assigned priority: Debian including 1 source packages (botan), 3 status rows across 3 suites (bookworm, bullseye, trixie): resolved 2, open 1. https://security-tracker.debian.org/tracker/CVE-2021-40529
gentoo high CVE-2021-40529: 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-2021-40529
ubuntu low CVE-2021-40529 low priority: Ubuntu including 2 source packages (botan, botan1.10), 30 status rows across 15 suites (bionic, focal, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): DNE 12, needs-triage 7, not-affected 6, ignored 4, released 1. https://ubuntu.com/security/CVE-2021-40529

Affected software / configurations for CVE-2021-40529

Vendor Product Version Raw CPE
botan_project botan <= 2.18.1 cpe:2.3:a:botan_project:botan:*:*:*:*:*:*:*:*
fedoraproject fedora 34 cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
fedoraproject fedora 35 cpe:2.3:o:fedoraproject:fedora:35:*:*:*:*:*:*:*
mozilla thunderbird < 91.12.0 cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*

References for CVE-2021-40529

cvelogic Threat Intelligence