# CVE-2021-40528: Weak cryptography in n/a

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

- **Severity:** Medium 5.9 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 6 Sep 2021
- **Updated:** 9 Jun 2025
- **Also known as:** ALPINE-CVE-2021-40528, ALSA-2022:5311, DEBIAN-CVE-2021-40528, DLA-2691-1, GHSA-8m2v-68m9-q2c7, JLSEC-2026-124, MGASA-2021-0446, OESA-2021-1362, RHSA-2022:5311, RLSA-2022:5311, UBUNTU-CVE-2021-40528, openSUSE-SU-2024:12540-1

## 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 (Use of a Broken or Risky Cryptographic Algorithm)

## Which versions are affected by CVE-2021-40528?

It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `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: 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.

## Other vulnerabilities in n/a

- [CVE-2021-3345](https://insights.sbomify.com/CVE-2021-3345/): Memory corruption in n/a (high 7.8)
- [CVE-2018-6829](https://insights.sbomify.com/CVE-2018-6829/): Weak cryptography in n/a (high 7.5)
- [CVE-2026-41989](https://insights.sbomify.com/CVE-2026-41989/): Memory corruption in Libgcrypt (medium 6.7)
- [CVE-2019-12904](https://insights.sbomify.com/CVE-2019-12904/): Information disclosure in n/a (medium 5.9)
- [CVE-2017-9526](https://insights.sbomify.com/CVE-2017-9526/): Information disclosure in n/a (medium 5.9)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-40528 and fix it if it is affected.

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

Affected product: n/a. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-40528/ (Markdown: https://insights.sbomify.com/CVE-2021-40528/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-40528
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-40528
- OSV: https://osv.dev/vulnerability/CVE-2021-40528

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-40528/
Summaries are generated and may contain mistakes; the official description above is the record.