# CVE-2026-34872: Weak cryptography in n/a

> Attackers can force shared secrets into small sets in FFDH due to improper input validation, compromising protocols relying on contributory behavior.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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:** 1 Apr 2026
- **Updated:** 1 Apr 2026
- **Also known as:** DEBIAN-CVE-2026-34872, ECHO-8e44-1e55-58a6, GHSA-347r-37hj-5jc9, JLSEC-2026-466, ROOT-OS-DEBIAN-12-CVE-2026-34872, UBUNTU-CVE-2026-34872

## What is CVE-2026-34872?

CVE-2026-34872 is a critical vulnerability in Arm Mbed Tls, published on 1 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

An issue was discovered in Mbed TLS 3.5.x and 3.6.x through 3.6.5 and TF-PSA-Crypto 1.0. There is a lack of contributory behavior in FFDH due to improper input validation. Using finite-field Diffie-Hellman, the other party can force the shared secret into a small set of values (lack of contributory behavior). This is a problem for protocols that depend on contributory behavior (which is not the case for TLS). The attack can be carried by the peer, or depending on the protocol by an active network attacker (person in the middle).

Weakness: CWE-347 (Improper Verification of Cryptographic Signature)

## Which versions are affected by CVE-2026-34872?

It affects 2 products.


Products: Arm Mbed Tls, Arm Tf-Psa-Crypto.

## How do I fix CVE-2026-34872?

Upgrade to a fixed version.

## Is CVE-2026-34872 being exploited?

There is no known exploitation of CVE-2026-34872 in the wild and no public exploit code.

## Other vulnerabilities in Arm Mbed Tls

- [CVE-2026-34877](https://insights.sbomify.com/CVE-2026-34877/): Deserialization in n/a (critical 9.8)
- [CVE-2022-46393](https://insights.sbomify.com/CVE-2022-46393/): Memory corruption in n/a (critical 9.8)
- [CVE-2021-44732](https://insights.sbomify.com/CVE-2021-44732/): Use after free in n/a (critical 9.8)
- [CVE-2017-18187](https://insights.sbomify.com/CVE-2017-18187/): Integer overflow in n/a (critical 9.8)
- [CVE-2018-0487](https://insights.sbomify.com/CVE-2018-0487/): Memory corruption in ARM mbed TLS before 1.3.22, before 2.1.10, and before 2.7.0 (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-34872 and fix it if it is affected.

What it is: CVE-2026-34872 is a critical vulnerability in Arm Mbed Tls, published on 1 Apr 2026. 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-2026-34872 in the wild and no public exploit code.

Affected product: Arm Mbed Tls. 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-2026-34872/ (Markdown: https://insights.sbomify.com/CVE-2026-34872/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-34872
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-34872
- OSV: https://osv.dev/vulnerability/CVE-2026-34872

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-34872/
Summaries are generated and may contain mistakes; the official description above is the record.