# CVE-2026-3849: Buffer Overflow in HPKE via Oversized ECH Config

> A malicious TLS server can trigger a stack buffer overflow in wolfSSL clients via oversized ECH configs, potentially enabling remote code execution or crashes.

- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N/V:D/RE:M/U:Amber`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 19 Mar 2026
- **Updated:** 25 Mar 2026
- **Also known as:** DEBIAN-CVE-2026-3849, GHSA-267h-vrw9-53p3, JLSEC-2026-711, UBUNTU-CVE-2026-3849

## What is CVE-2026-3849?

CVE-2026-3849 is a medium-severity memory corruption vulnerability in Wolfssl Wolfssl, published on 19 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Stack Buffer Overflow in wc_HpkeLabeledExtract via Oversized ECH Config. A vulnerability existed in wolfSSL 5.8.4 ECH (Encrypted Client Hello) support, where a maliciously crafted ECH config could cause a stack buffer overflow on the client side, leading to potential remote execution and client program crash. This could be exploited by a malicious TLS server supporting ECH. Note that ECH is off by default, and is only enabled with enable-ech.

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2026-3849?

It affects 1 product.


Products: Wolfssl Wolfssl.

## How do I fix CVE-2026-3849?

Apply the vendor's patch.

## Is CVE-2026-3849 being exploited?

There is no known exploitation of CVE-2026-3849 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-2026-3849 and fix it if it is affected.

What it is: CVE-2026-3849 is a medium-severity memory corruption vulnerability in Wolfssl Wolfssl, published on 19 Mar 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-2026-3849 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-2026-3849/ (Markdown: https://insights.sbomify.com/CVE-2026-3849/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-3849
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-3849
- OSV: https://osv.dev/vulnerability/CVE-2026-3849

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-3849/
Summaries are generated and may contain mistakes; the official description above is the record.