---
title: "CVE-2025-66565: Fiber Utils UUIDv4 and UUID Silent Fallback to Predictable Values"
url: https://erroneo.us/security/cve/CVE-2025-66565/
description: "CVE-2025-66565 (github.com/gofiber/utils/v2 (Go)): Fiber Utils is a collection of common functions created for Fiber. In versions 2.0.0-rc.3 and below, when…"
type: vulnerability-record
section: "Security Digest"
date_published: 2025-12-09
date_modified: 2025-12-12
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2025-66565"
kev: false
cvss: 9.3
epss: 0.00468
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2025-66565: Fiber Utils UUIDv4 and UUID Silent Fallback to Predictable Values

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Not in CISA KEV , but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
- EPSS 0.5% , percentile 39: FIRST’s model estimates a 0.5% chance of exploitation activity in the next 30 days, higher than 39% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes github.com/gofiber/utils/v2 (Go) < 2.0.0-rc.3.0.20251205210924-6c6cf047032b, fixed in 2.0.0-rc.4 ; github.com/gofiber/utils (Go) <= 1.1.0, fixed in 1.2.0 . Check your lockfile, including transitive dependencies.

## What it is

Fiber Utils is a collection of common functions created for Fiber. In versions 2.0.0-rc.3 and below, when the system's cryptographic random number generator (crypto/rand) fails, both functions silently fall back to returning predictable UUID values, including the zero UUID "00000000-0000-0000-0000-000000000000". The vulnerability occurs through two related but distinct failure paths, both ultimately caused by crypto/rand.Read() failures, compromising the security of all Fiber applications using these functions for security-critical operations. This issue is fixed in version 2.0.0-rc.4.

## Affected packages

- Go `github.com/gofiber/utils/v2` < 2.0.0-rc.3.0.20251205210924-6c6cf047032b → fixed: 2.0.0-rc.4
- Go `github.com/gofiber/utils` <= 1.1.0 → fixed: 1.2.0

## Affected products (CVE record)

- gofiber utils: github.com/gofiber/utils <= 1.2.0, github.com/gofiber/utils/v2 < 2.0.0-rc.4

## Severity

- GitHub_M CVSS 4.0: 9.3 `CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N`
- GitHub CVSS 4.0: 9.2 `CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation poc , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.47% probability of exploitation activity in the next 30 days; percentile 39.

## Sources

- [GitHub Advisory GHSA-m98w-cqp3-qcqr](https://github.com/advisories/GHSA-m98w-cqp3-qcqr)
- [CVE.org record CVE-2025-66565](https://www.cve.org/CVERecord?id=CVE-2025-66565)
- [NVD entry CVE-2025-66565](https://nvd.nist.gov/vuln/detail/CVE-2025-66565)
- [github.com](https://github.com/gofiber/utils/security/advisories/GHSA-m98w-cqp3-qcqr)
- [github.com](https://github.com/gofiber/utils/commit/6c6cf047032b9c8dff43d29f990b4b10e9b02d47)

---
Source page: https://erroneo.us/security/cve/CVE-2025-66565/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt