# CVE-2026-34876: Information disclosure in n/a

> Attackers can read adjacent memory via oversized tag_len in Mbed TLS CCM API, potentially exposing sensitive context data.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/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:** 2 Apr 2026
- **Updated:** 2 Apr 2026
- **Also known as:** DEBIAN-CVE-2026-34876, ECHO-2b14-d1fe-8a7a, GHSA-jw9g-6hxw-4whq, UBUNTU-CVE-2026-34876

## What is CVE-2026-34876?

CVE-2026-34876 is a high-severity vulnerability in n/a, 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 3.x before 3.6.6. An out-of-bounds read vulnerability in mbedtls_ccm_finish() in library/ccm.c allows attackers to obtain adjacent CCM context data via invocation of the multipart CCM API with an oversized tag_len parameter. This is caused by missing validation of the tag_len parameter against the size of the internal 16-byte authentication buffer. The issue affects the public multipart CCM API in Mbed TLS 3.x, where mbedtls_ccm_finish() can be invoked directly by applications. In Mbed TLS 4.x versions prior to the fix, the same missing validation exists in the internal implementation; however, the function is not exposed as part of the public API. Exploitation requires application-level invocation of the multipart CCM API.

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-34876?

It affects 1 product.


Products: Trustedfirmware Mbed Tls.

## How do I fix CVE-2026-34876?

Upgrade to a fixed version.

## Is CVE-2026-34876 being exploited?

There is no known exploitation of CVE-2026-34876 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2026-34875](https://insights.sbomify.com/CVE-2026-34875/): Memory corruption in n/a (critical 9.8)
- [CVE-2024-49195](https://insights.sbomify.com/CVE-2024-49195/): Memory corruption in n/a (critical 9.8)
- [CVE-2024-45158](https://insights.sbomify.com/CVE-2024-45158/): Memory corruption in n/a (critical 9.8)
- [CVE-2024-45159](https://insights.sbomify.com/CVE-2024-45159/): Auth bypass in n/a (critical 9.8)
- [CVE-2023-45199](https://insights.sbomify.com/CVE-2023-45199/): Mbed TLS 3.2.x through 3.4.x before 3.5 has a Buffer Overflow that can lead to remote Code execution. (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-34876 and fix it if it is affected.

What it is: CVE-2026-34876 is a high-severity vulnerability in n/a, 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-2026-34876 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-2026-34876/ (Markdown: https://insights.sbomify.com/CVE-2026-34876/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-34876
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-34876
- OSV: https://osv.dev/vulnerability/CVE-2026-34876

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-34876/
Summaries are generated and may contain mistakes; the official description above is the record.