What’s Vulnerable › Vulnerabilities
CVE-2021-40529
- Severity: medium (CVSS 5.9 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 1.5% probability of exploitation in the next 30 days
- Public exploit or detection template: yes
- Published: 2021-09-06 · updated 2026-06-17
- Weakness: CWE-327
Description
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.
Affected products
- randombit botan: through 2.18.1
- Fedoraproject Fedora: 34, 35
- Mozilla Thunderbird: before 91.12.0 — fixed in 91.12.0
How to fix
Upgrade to a fixed version: Mozilla Thunderbird 91.12.0. Check the vendor advisory for mitigations.
References
- https://eprint.iacr.org/2021/923
- https://github.com/randombit/botan/pull/2790
- https://ibm.github.io/system-security-research-updates/2021/07/20/insecurity-elgamal-pt1
- https://ibm.github.io/system-security-research-updates/2021/09/06/insecurity-elgamal-pt2
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/72NB4OLD3VHJC3YF3PEP2HKF6BYURPAO/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/UPHGYWNJQKWLTUWBNSFB4F66MQDIL3IB/
- https://security.gentoo.org/glsa/202208-14
- https://eprint.iacr.org/2021/923
- https://github.com/randombit/botan/pull/2790
- https://ibm.github.io/system-security-research-updates/2021/07/20/insecurity-elgamal-pt1
- https://ibm.github.io/system-security-research-updates/2021/09/06/insecurity-elgamal-pt2
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/72NB4OLD3VHJC3YF3PEP2HKF6BYURPAO/
Get alerted when CVE-2021-40529 or the next vulnerability affects your stack