# CVE-2026-8720: HMAC-BLAKE2 final discards message when key length exceeds block size

> wolfSSL HMAC-BLAKE2 implementation ignores message data when keys exceed block size, allowing attackers to bypass integrity checks.

- **Severity:** Medium 5.9 (`CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 25 Jun 2026
- **Updated:** 26 Jun 2026
- **Also known as:** DEBIAN-CVE-2026-8720, GHSA-34qm-63x6-fcm3, UBUNTU-CVE-2026-8720

## What is CVE-2026-8720?

CVE-2026-8720 is a medium-severity vulnerability in Wolfssl Wolfssl, published on 25 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

wc_Blake2bHmacFinal and wc_Blake2sHmacFinal discard the message when the key length exceeds the block size, producing a MAC that is independent of the input. When the supplied key is longer than the BLAKE2 block size the key-hashing branch reinitialized the running hash state, discarding the accumulated message data, so the resulting MAC depended only on the key and not on the message being authenticated. This bug is specific to the HMAC-BLAKE2 APIs that were added in wolfSSL version 5.9.0.

Weakness: CWE-354 (Improper Validation of Integrity Check Value)

## Which versions are affected by CVE-2026-8720?

It affects 1 product.


Products: Wolfssl Wolfssl.

## How do I fix CVE-2026-8720?

No fix has been published for CVE-2026-8720 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-8720 being exploited?

There is no known exploitation of CVE-2026-8720 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-2026-8720 and fix it if it is affected.

What it is: CVE-2026-8720 is a medium-severity vulnerability in Wolfssl Wolfssl, published on 25 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-8720 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-2026-8720/ (Markdown: https://insights.sbomify.com/CVE-2026-8720/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-8720
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-8720
- OSV: https://osv.dev/vulnerability/CVE-2026-8720

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-8720/
Summaries are generated and may contain mistakes; the official description above is the record.