# CVE-2021-40529: Weak cryptography in n/a

> A flaw in Botan's ElGamal implementation allows plaintext recovery via cross-configuration attacks, impacting applications like Thunderbird.

- **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:** 4 Aug 2024
- **Also known as:** ALPINE-CVE-2021-40529, DEBIAN-CVE-2021-40529, GHSA-f9qg-252f-g8cg, MGASA-2021-0563, UBUNTU-CVE-2021-40529, openSUSE-SU-2024:11661-1

## What is CVE-2021-40529?

CVE-2021-40529 is a medium-severity vulnerability in Fedoraproject Fedora, 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 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.

Weakness: CWE-327 (Use of a Broken or Risky Cryptographic Algorithm)

## Which versions are affected by CVE-2021-40529?

It affects 3 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `Botan` | openSUSE:Tumbleweed | All versions | 2.18.2-1.1 |

Products: Botan Project Botan, Fedoraproject Fedora, Mozilla Thunderbird.

## How do I fix CVE-2021-40529?

Upgrade to a fixed version.

## Is CVE-2021-40529 being exploited?

There is no known exploitation of CVE-2021-40529 in the wild and no public exploit code.

## Other vulnerabilities in Fedoraproject Fedora

- [CVE-2021-24115](https://insights.sbomify.com/CVE-2021-24115/): Information disclosure in n/a (critical 9.8)
- [CVE-2018-9127](https://insights.sbomify.com/CVE-2018-9127/): Security feature bypass in n/a (critical 9.8)
- [CVE-2015-7826](https://insights.sbomify.com/CVE-2015-7826/): Security feature bypass in n/a (critical 9.8)
- [CVE-2016-6878](https://insights.sbomify.com/CVE-2016-6878/): Other in n/a (critical 9.8)
- [CVE-2016-9132](https://insights.sbomify.com/CVE-2016-9132/): Integer overflow in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-40529 and fix it if it is affected.

What it is: CVE-2021-40529 is a medium-severity vulnerability in Fedoraproject Fedora, 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-2021-40529 in the wild and no public exploit code.

Affected product: Fedoraproject Fedora. 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-2021-40529/ (Markdown: https://insights.sbomify.com/CVE-2021-40529/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-40529
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-40529
- OSV: https://osv.dev/vulnerability/CVE-2021-40529

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-40529/
Summaries are generated and may contain mistakes; the official description above is the record.