---
title: "CVE-2026-34877\n    | Ubuntu"
description: Ubuntu is an open source software operating system that runs from the
  desktop, to the cloud, to all your internet connected things.
url: https://ubuntu.com/security/CVE-2026-34877?format=md
keywords: index, follow
---

# CVE-2026-34877

Publication date 2 April 2026

Last updated 8 April 2026

---

Ubuntu priority

**Medium**

[Why this priority?](https://ubuntu.com/security/cves/about#priority )

## Cvss 3 Severity Score

**9.8 · Critical**

[Score breakdown](https://ubuntu.com/security/CVE-2026-34877?format=md#impact-score)

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## 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.

## Status

Show unmaintained releases

| Package | Ubuntu Release | Status |
| --- | --- | --- |
| mbedtls | 26.04 LTS resolute | Needs evaluation |
| 25.10 questing | Ignored end of life, was needs-triage |
| 24.04 LTS noble | Needs evaluation |
| 22.04 LTS jammy | Needs evaluation |
| 20.04 LTS focal | Needs evaluation |
| 18.04 LTS bionic | Needs evaluation |
| 16.04 LTS xenial | Needs evaluation |

---

* [How can I get the fixes?](https://ubuntu.com/security/cves/about#security)
* [What do statuses mean?](https://ubuntu.com/security/cves/about#statuses)

## Severity score breakdown

CVSS version:
CVSS v3.0

**Base score**

9.8 · Critical

* Base metrics

  | Parameter | Value |
  | --- | --- |
  | Attack vector | Network |
  | Attack complexity | Low |
  | Privileges required | None |
  | User interaction | None |
  | Scope | Unchanged |
  | Confidentiality impact | High |
  | Integrity impact | High |
  | Availability impact | High |
* Scores

  | Parameter | Value |
  | --- | --- |
  | Base score | 9.8 · Critical |
  | Exploitability score | - |
  | Impact score | - |

**Vector:** CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

## References

* [MITRE](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2026-34877)
* [NVD](https://nvd.nist.gov/vuln/detail/CVE-2026-34877)
* [Launchpad](https://launchpad.net/bugs/cve/CVE-2026-34877)
* [Debian](https://security-tracker.debian.org/tracker/CVE-2026-34877)

### Other references

* <https://www.cve.org/CVERecord?id=CVE-2026-34877>
* <https://mbed-tls.readthedocs.io/en/latest/security-advisories/mbedtls-security-advisory-2026-03-serialized-data/>