Four days ago, security researcher ReneWerner87 revealed GHSA-68rr-p4fp-j59v, a serious flaw in the widely used Fiber v2 web framework that should serve as a major wake-up call for Go developers This article explores secure randomness fiber. . This vulnerability, known as CVE-2025-66630, is caused by the internal gofiber/utils module of Fiber v2, where UUIDv4() and UUID() functions produce predictable or all-zero UUIDs (such as 00000000-0000-0000-0000-000000000000) when Go's crypto/rand is unable to provide secure randomness.

Fiber v2, a quick framework for Go that was inspired by Express, offers its own utility package. If crypto/rand is unable to access strong randomness from sources such as /dev/urandom on Go versions prior to 1.24, it returns an error. Fiber's UUID functions silently revert to weak, predictable values rather than failing audibly.

Fiber v2 still supports older Go runtimes (up to 1.23), leaving apps vulnerable. Go 1.24+ fixes this by blocking or panicking on entropy shortages. This is a security disaster, not just a small bug.

By default, a lot of Fiber middleware depends on these UUIDs, including request IDs, rate limiting, CSRF protection, and session management. Attackers can replay auth tokens, forge CSRF tokens to get around security measures, predict session IDs for hijacking, or cause a denial of service attack by directing all traffic into a single "zero-key" bucket. This overwhelms systems by corrupting caches, sessions, and locks. The problem is most prevalent in complex environments, such as embedded devices, chroot jails, Docker containers, or incorrectly configured servers with low entropy.

While limited setups frequently result in failures, modern Linux kernels rarely lack randomness.

Description of Metric Value CVE ID: CVE-2025-66630 assigned identifier for the defect. Score of 8.2 (High) on CVSS v4 Base: AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N All Fiber v2 versions prior to 2.52.11 are impacted; update to 2.52.11 right away. For the vendored utils, there is currently no upstream fix.

Reductions: Upgrade to Fiber v2. Examine UUID usage in older Go and swap it out for secure substitutes like github.com/google/uuid. Test in low-entropy simulations, such as simulated crypto/rand errors. Check logs for no UUIDs.

This defect highlights an important lesson: Crypto code silent fallbacks can be harmful. Randomness must be explicitly verified by developers. It is recommended that fiber maintainers remove the outdated utilities and conform to Go's contemporary guarantees.