# CVE-2026-34877: Deserialization in n/a

> Attackers can achieve arbitrary code execution by modifying serialized SSL context or session structures in Mbed TLS.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 2 Apr 2026
- **Updated:** 2 Apr 2026
- **Also known as:** DEBIAN-CVE-2026-34877, GHSA-xg3m-c464-j5fh, JLSEC-2026-467, UBUNTU-CVE-2026-34877

## What is CVE-2026-34877?

CVE-2026-34877 is a critical unsafe deserialization vulnerability in Arm Mbed Tls, published on 2 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 versions from 2.19.0 up to 3.6.5, Mbed TLS 4.0.0. Insufficient protection of serialized SSL context or session structures allows an attacker who can modify the serialized structures to induce memory corruption, leading to arbitrary code execution. This is caused by Incorrect Use of Privileged APIs.

Weakness: CWE-502 (Deserialization of Untrusted Data), CWE-250 (Execution with Unnecessary Privileges)

## Which versions are affected by CVE-2026-34877?

It affects 2 products.


Products: Arm Mbed Tls, Trustedfirmware Mbed Tls.

## How do I fix CVE-2026-34877?

Upgrade to a fixed version.

## Is CVE-2026-34877 being exploited?

There is no known exploitation of CVE-2026-34877 in the wild and no public exploit code.

## Other vulnerabilities in Arm Mbed Tls

- [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)
- [CVE-2018-0488](https://insights.sbomify.com/CVE-2018-0488/): 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-2026-34877 and fix it if it is affected.

What it is: CVE-2026-34877 is a critical unsafe deserialization vulnerability in Arm Mbed Tls, published on 2 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-2026-34877 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-2026-34877/ (Markdown: https://insights.sbomify.com/CVE-2026-34877/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-34877
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-34877
- OSV: https://osv.dev/vulnerability/CVE-2026-34877

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-34877/
Summaries are generated and may contain mistakes; the official description above is the record.