# CVE-2026-5477: Prefix-substitution forgery via integer overflow in wolfCrypt CMAC

> An integer overflow in wolfCrypt CMAC allows attackers to forge authentication tags via prefix substitution, compromising data integrity.

- **Severity:** High 8.2 (`CVSS:4.0/AV:N/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:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 10 Apr 2026
- **Updated:** 10 Apr 2026
- **Also known as:** DEBIAN-CVE-2026-5477, GHSA-grqc-3vmg-p68x, JLSEC-2026-727, UBUNTU-CVE-2026-5477

## What is CVE-2026-5477?

CVE-2026-5477 is a high-severity vulnerability in Wolfssl Wolfssl, published on 10 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

An integer overflow existed in the wolfCrypt CMAC implementation, that could be exploited to forge CMAC tags. The function wc_CmacUpdate used the guard `if (cmac->totalSz != 0)` to skip XOR-chaining on the first block (where digest is all-zeros and the XOR is a no-op). However, totalSz is word32 and wraps to zero after 2^28 block flushes (4 GiB), causing the guard to erroneously discard the live CBC-MAC chain state. Any two messages sharing a common suffix beyond the 4 GiB mark then produce identical CMAC tags, enabling a zero-work prefix-substitution forgery. The fix removes the guard, making the XOR unconditional; the no-op property on the first block is preserved because digest is zero-initialized by wc_InitCmac_ex.

Weakness: CWE-190 (Integer Overflow or Wraparound)

## Which versions are affected by CVE-2026-5477?

It affects 1 product.


Products: Wolfssl Wolfssl.

## How do I fix CVE-2026-5477?

Apply the vendor's patch.

## Is CVE-2026-5477 being exploited?

There is no known exploitation of CVE-2026-5477 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-2026-5477 and fix it if it is affected.

What it is: CVE-2026-5477 is a high-severity vulnerability in Wolfssl Wolfssl, published on 10 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-2026-5477 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-2026-5477/ (Markdown: https://insights.sbomify.com/CVE-2026-5477/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-5477
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-5477
- OSV: https://osv.dev/vulnerability/CVE-2026-5477

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-5477/
Summaries are generated and may contain mistakes; the official description above is the record.