CVE-2021-40528 Weak cryptography in n/a

Medium 5.9 Published 6 Sep 2021 Updated 9 Jun 2025

A flaw in Libgcrypt's ElGamal implementation allows plaintext recovery via cross-configuration attacks, impacting OpenPGP users.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: Available

What is CVE-2021-40528?

CVE-2021-40528 is a medium-severity vulnerability in n/a, published on 6 Sep 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official 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.

Weakness: CWE-327

Which versions are affected by CVE-2021-40528?

It affects 1 product.

Linux distribution packages (9)

`libgcrypt` AlmaLinux:8	All versions	`1.8.5-7.el8_6`
`libgcrypt-devel` AlmaLinux:8	All versions	`1.8.5-7.el8_6`
`libgcrypt` Red Hat:enterprise_linux:8::baseos	All versions	`0:1.8.5-7.el8_6`
`libgcrypt-debuginfo` Red Hat:enterprise_linux:8::baseos	All versions	`0:1.8.5-7.el8_6`
`libgcrypt-debugsource` Red Hat:enterprise_linux:8::baseos	All versions	`0:1.8.5-7.el8_6`
`libgcrypt-devel` Red Hat:enterprise_linux:8::baseos	All versions	`0:1.8.5-7.el8_6`
`libgcrypt-devel-debuginfo` Red Hat:enterprise_linux:8::baseos	All versions	`0:1.8.5-7.el8_6`
`libgcrypt` Rocky Linux:8	All versions	`0:1.8.5-7.el8_6`
`libgcrypt` openSUSE:Tumbleweed	All versions	`1.10.1-1.1`

Products include Gnupg Libgcrypt.

How do I fix CVE-2021-40528?

Upgrade to a fixed version.

Is CVE-2021-40528 being exploited?

There is no known exploitation of CVE-2021-40528 in the wild and no public exploit code.

Sources

Also known as ALPINE-CVE-2021-40528, ALSA-2022:5311, DEBIAN-CVE-2021-40528, DLA-2691-1, GHSA-8m2v-68m9-q2c7, JLSEC-2026-124 and 6 more.