# CVE-2023-6936: Heap-buffer over-read with WOLFSSL_CALLBACKS

> A heap buffer over-read in wolfSSL allows attackers to read memory or cause crashes when debugging callbacks are enabled.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/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:** 20 Feb 2024
- **Updated:** 26 Mar 2025
- **Also known as:** DEBIAN-CVE-2023-6936, GHSA-cwpg-8775-j56v, JLSEC-2026-678, UBUNTU-CVE-2023-6936

## What is CVE-2023-6936?

CVE-2023-6936 is a medium-severity memory corruption vulnerability in Wolfssl Wolfssl, published on 20 Feb 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In wolfSSL prior to 5.6.6, if callback functions are enabled (via the WOLFSSL_CALLBACKS flag), then a malicious TLS client or network attacker can trigger a buffer over-read on the heap of 5 bytes (WOLFSSL_CALLBACKS is only intended for debugging).

Weakness: CWE-125 (Out-of-bounds Read), CWE-126 (Buffer Over-read)

## Which versions are affected by CVE-2023-6936?

It affects 1 product.


Products: Wolfssl Wolfssl.

## How do I fix CVE-2023-6936?

Upgrade to a fixed version.

## Is CVE-2023-6936 being exploited?

There is no known exploitation of CVE-2023-6936 in the wild and no public exploit code.

## Other vulnerabilities in Wolfssl Wolfssl

- [CVE-2024-5991](https://insights.sbomify.com/CVE-2024-5991/): Buffer overread in domain name matching (critical 10.0)
- [CVE-2021-37155](https://insights.sbomify.com/CVE-2021-37155/): Security feature bypass in n/a (critical 9.8)
- [CVE-2020-36177](https://insights.sbomify.com/CVE-2020-36177/): Memory corruption in n/a (critical 9.8)
- [CVE-2014-2896](https://insights.sbomify.com/CVE-2014-2896/): Memory corruption in n/a (critical 9.8)
- [CVE-2014-2897](https://insights.sbomify.com/CVE-2014-2897/): Memory corruption in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-6936 and fix it if it is affected.

What it is: CVE-2023-6936 is a medium-severity memory corruption vulnerability in Wolfssl Wolfssl, published on 20 Feb 2024. 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-2023-6936 in the wild and no public exploit code.

Affected product: Wolfssl Wolfssl. 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-2023-6936/ (Markdown: https://insights.sbomify.com/CVE-2023-6936/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-6936
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-6936
- OSV: https://osv.dev/vulnerability/CVE-2023-6936

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-6936/
Summaries are generated and may contain mistakes; the official description above is the record.