CVE-2021-40529

Name: CVE-2021-40529
Creator: NVD / NIST
Published: 2021-09-06T19:15:07.63+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 5.9/10EPSS 1.48%

Last modified Jun 17, 2026

CVE-2021-40529 is a medium-severity vulnerability rated 5.9/10 on the CVSS scale. 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.. EPSS estimates a 1.48% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

5.9/10

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

EPSS Probability

1.48%

70.7th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-327

Affected Software

Vendor	Product	Versions
Botan Project	Botan	<= 2.18.1
Fedoraproject	Fedora	34
Fedoraproject	Fedora	35
Mozilla	Thunderbird	< 91.12.0

References

https://eprint.iacr.org/2021/923Technical Description, Third Party Advisory
https://github.com/randombit/botan/pull/2790Patch, Third Party Advisory
https://ibm.github.io/system-security-research-updates/2021/07/20/insecurity-elgamal-pt1Third Party Advisory
https://ibm.github.io/system-security-research-updates/2021/09/06/insecurity-elgamal-pt2Exploit, Third Party Advisory
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/202208-14Third Party Advisory
https://eprint.iacr.org/2021/923Technical Description, Third Party Advisory
https://github.com/randombit/botan/pull/2790Patch, Third Party Advisory
https://ibm.github.io/system-security-research-updates/2021/07/20/insecurity-elgamal-pt1Third Party Advisory
https://ibm.github.io/system-security-research-updates/2021/09/06/insecurity-elgamal-pt2Exploit, Third Party Advisory
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/202208-14Third Party Advisory

Timeline

Published: Sep 6, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-40529?

How severe is CVE-2021-40529?

CVE-2021-40529 has a CVSS score of 5.9/10 (MEDIUM severity). The EPSS model estimates a 1.48% probability of exploitation in the next 30 days.

How do I fix CVE-2021-40529?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-40529?

Run a free Strix scan to check your systems for this vulnerability.

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Source: NVD / NIST