CVE-2021-40528

Name: CVE-2021-40528
Creator: NVD / NIST
Published: 2021-09-06T19:15:07.587+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 5.9/10EPSS 1.32%

Last modified Jun 17, 2026

CVE-2021-40528 is a medium-severity vulnerability rated 5.9/10 on the CVSS scale. The ElGamal implementation in Libgcrypt before 1.9.4 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 1.32% chance of exploitation in the next 30 days.

Description

The ElGamal implementation in Libgcrypt before 1.9.4 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

1.32%

67.3th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Gnupg	Libgcrypt	< 1.9.4

References

https://eprint.iacr.org/2021/923Technical Description, Third Party Advisory
https://git.gnupg.org/cgi-bin/gitweb.cgi?p=libgcrypt.git%3Ba=commit%3Bh=3462280f2e23e16adf3ed5176e0f2413d8861320
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://security.gentoo.org/glsa/202210-13Third Party Advisory
https://eprint.iacr.org/2021/923Technical Description, Third Party Advisory
https://git.gnupg.org/cgi-bin/gitweb.cgi?p=libgcrypt.git%3Ba=commit%3Bh=3462280f2e23e16adf3ed5176e0f2413d8861320
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://security.gentoo.org/glsa/202210-13Third Party Advisory

Timeline

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

Frequently Asked Questions

What is CVE-2021-40528?

How severe is CVE-2021-40528?

CVE-2021-40528 has a CVSS score of 5.9/10 (MEDIUM severity). The EPSS model estimates a 1.32% probability of exploitation in the next 30 days.

How do I fix CVE-2021-40528?

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-2021-40528?

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

Scan your code now

Source: NVD / NIST