Critical UUID Flaw in Fiber v2 on Go 1.24+ Enables Session Hijacking and CSRF Bypass

In a major wake-up call for Go developers, security researcher ReneWerner87 disclosed GHSA-68rr-p4fp-j59v four days ago, exposing a critical vulnerability in the popular Fiber v2 web framework.

Dubbed CVE-2025-66630, this flaw stems from Fiber v2’s internal gofiber/utils module, where UUIDv4() and UUID() functions generate predictable or all-zero UUIDs (like 00000000-0000-0000-0000-000000000000) when Go’s crypto/rand fails to provide secure randomness.

Fiber v2, a fast Express-inspired framework for Go, vendors its own utils package. On Go versions before 1.24, crypto/rand returns an error if it can’t access strong randomness from sources like /dev/urandom.

Instead of failing loudly, Fiber’s UUID functions silently fall back to weak, predictable values. Go 1.24+ fixes this by blocking or panicking on entropy shortages, but Fiber v2 still supports older Go runtimes (up to 1.23), leaving apps exposed.

This isn’t just a minor glitch; it’s a security catastrophe. Many Fiber middleware, like session management, CSRF protection, rate limiting, and request IDs, rely on these UUIDs by default.

Attackers can predict session IDs for hijacking, forge CSRF tokens to bypass protections, replay auth tokens, or trigger DoS by forcing all traffic into a single “zero-key” bucket. This corrupts caches, sessions, and locks, overwhelming systems.

The issue hits hardest in tricky environments: Docker containers, chroot jails, embedded devices, or misconfigured servers low on entropy.

Modern Linux kernels rarely starve for randomness, but restricted setups make failures common.

Metric	Value	Description
CVE ID	CVE-2025-66630	Assigned identifier for the flaw.
CVSS v4 Score	8.2 (High)	Base: AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N

Affected versions are all Fiber v2 before 2.52.11; patch to 2.52.11 immediately. No upstream fix exists yet for the vendored utils.

Mitigations: Upgrade Fiber v2. For older Go, audit UUID usage, replace with safe alternatives like github.com/google/uuid. Test in low-entropy sims (e.g., mock crypto/rand errors). Monitor logs for zero UUIDs.

This flaw underscores a key lesson: Silent fallbacks in crypto code are dangerous. Developers must validate randomness explicitly. Fiber maintainers are urged to rip out the weak utils and align with Go’s modern guarantees.

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