---
title: "CVE-2026-5477\n    | Ubuntu"
description: Ubuntu is an open source software operating system that runs from the
  desktop, to the cloud, to all your internet connected things.
url: https://ubuntu.com/security/CVE-2026-5477?format=md
keywords: index, follow
---

# CVE-2026-5477

Publication date 10 April 2026

Last updated 10 July 2026

---

Ubuntu priority

**Medium**

[Why this priority?](https://ubuntu.com/security/cves/about#priority )

## Cvss 3 Severity Score

**7.5 · High**

[Score breakdown](https://ubuntu.com/security/CVE-2026-5477?format=md#impact-score)

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## 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.

## Status

Show unmaintained releases

| Package | Ubuntu Release | Status |
| --- | --- | --- |
| wolfssl | 26.04 LTS resolute | Needs evaluation |
| 25.10 questing | Ignored end of life, was needs-triage |
| 24.04 LTS noble | Needs evaluation |
| 22.04 LTS jammy | Needs evaluation |
| 20.04 LTS focal | Needs evaluation |
| 18.04 LTS bionic | Needs evaluation |
| 16.04 LTS xenial | Needs evaluation |

---

* [How can I get the fixes?](https://ubuntu.com/security/cves/about#security)
* [What do statuses mean?](https://ubuntu.com/security/cves/about#statuses)

## Severity score breakdown

CVSS version:

CVSS v4.0

[CVSS v4.0](https://ubuntu.com/security/CVE-2026-5477?format=md)
[CVSS v3.0](https://ubuntu.com/security/CVE-2026-5477?format=md)

**Base score**

8.2 · High

* Base metrics

  | Parameter | Value |
  | --- | --- |
  | Attack vector | Network |
  | Attack complexity | Low |
  | Attack requirements | Present |
  | Privileges required | None |
  | User interaction | None |
  | Vulnerable system - Confidentiality impact | None |
  | Vulnerable system - Integrity impact | High |
  | Vulnerable system - Availability impact | None |
  | Subsequent system - Confidentiality impact | None |
  | Subsequent system - Integrity impact | None |
  | Subsequent system - Availability impact | None |
* Scores

  | Parameter | Value |
  | --- | --- |
  | Base score | 8.2 · High |
  | Base + Threat score | - |
  | Base + Environmental score | - |
  | Base + Threat + Environmental score | - |

**Vector:** 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

## References

* [MITRE](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2026-5477)
* [NVD](https://nvd.nist.gov/vuln/detail/CVE-2026-5477)
* [Launchpad](https://launchpad.net/bugs/cve/CVE-2026-5477)
* [Debian](https://security-tracker.debian.org/tracker/CVE-2026-5477)

### Other references

* <https://www.cve.org/CVERecord?id=CVE-2026-5477>
* <https://github.com/wolfSSL/wolfssl/pull/10102>