# CVE-2026-3547: wolfSSL: out-of-bounds read (DoS) in ALPN parsing due to incomplete validation

> A crafted ALPN protocol list can cause an out-of-bounds read and crash in wolfSSL when ALPN is enabled, requiring a patch.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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:** 19 Mar 2026
- **Updated:** 21 Mar 2026
- **Also known as:** DEBIAN-CVE-2026-3547, GHSA-f377-557w-vjgv, JLSEC-2026-706, UBUNTU-CVE-2026-3547

## What is CVE-2026-3547?

CVE-2026-3547 is a high-severity denial of service 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

Out-of-bounds read in ALPN parsing due to incomplete validation. wolfSSL 5.8.4 and earlier contained an out-of-bounds read in ALPN handling when built with ALPN enabled (HAVE_ALPN / --enable-alpn). A crafted ALPN protocol list could trigger an out-of-bounds read, leading to a potential process crash (denial of service). Note that ALPN is disabled by default, but is enabled for these 3rd party compatibility features: enable-apachehttpd, enable-bind, enable-curl, enable-haproxy, enable-hitch, enable-lighty, enable-jni, enable-nginx, enable-quic.

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

## Which versions are affected by CVE-2026-3547?

It affects 1 product.


Products: Wolfssl Wolfssl.

## How do I fix CVE-2026-3547?

Apply the vendor's patch.

## Is CVE-2026-3547 being exploited?

There is no known exploitation of CVE-2026-3547 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-2026-3547 and fix it if it is affected.

What it is: CVE-2026-3547 is a high-severity denial of service 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-2026-3547 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-2026-3547/ (Markdown: https://insights.sbomify.com/CVE-2026-3547/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-3547
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-3547
- OSV: https://osv.dev/vulnerability/CVE-2026-3547

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-3547/
Summaries are generated and may contain mistakes; the official description above is the record.