CVE-2025-66630

Fiber v2 contains an internal vendored copy of gofiber/utils, and its functions UUIDv4() and UUID() inherit the same critical weakness described in the upstream advisory. On Go versions prior to 1.24, the underlying crypto/rand implementation can return an error if secure randomness cannot be obtained. In such cases, these Fiber v2 UUID functions silently fall back to generating predictable values, the all-zero UUID 00000000-0000-0000-0000-000000000000.

On Go 1.24+, the language guarantees that crypto/rand no longer returns an error (it will block or panic instead), so this vulnerability primarily affects Fiber v2 users running Go 1.23 or earlier, which Fiber v2 officially supports.

Because no error is returned by the Fiber v2 UUID functions, application code may unknowingly rely on predictable, repeated, or low-entropy identifiers in security-critical pathways. This is especially impactful because many Fiber v2 middleware components (session middleware, CSRF, rate limiting, request-ID generation, etc.) default to using utils.UUIDv4().

Impact includes, but is not limited to:

• Session fixation or hijacking (predictable session IDs)
• CSRF token forgery or bypass
• Authentication replay / token prediction
• Potential denial-of-service (DoS): if the zero UUID is generated, key-based structures (sessions, rate-limits, caches, CSRF stores) may collapse into a single shared key, causing overwrites, lock contention, or state corruption
• Request-ID collisions, undermining logging and trace integrity
• General compromise of confidentiality, integrity, and authorization logic relying on UUIDs for uniqueness or secrecy

All Fiber v2 versions containing the internal utils.UUIDv4() / utils.UUID() implementation are affected when running on Go <1.24. No patched Fiber v2 release currently exists.

Suggested Mitigations / Workarounds

Update to the latest version of Fiber v2.

Likelihood / Environmental Factors

It’s important to note that entropy exhaustion on modern Linux systems is extremely rare, as the kernel’s CSPRNG is resilient and non-blocking. However, entropy-source failures, where crypto/rand cannot read from its underlying provider, are significantly more likely in certain environments.

This includes containerized deployments, restricted sandboxes, misconfigured systems lacking read access to /dev/urandom or platform-equivalent sources, chrooted or jailed environments, embedded devices, or systems with non-standard or degraded randomness providers. On Go <1.24, such failures cause crypto/rand to return an error, which the Fiber v2 UUID functions currently treat as a signal to silently generate predictable UUIDs, including the zero UUID. This silent fallback is the root cause of the vulnerability.

References

• Upstream advisory for gofiber/utils: GHSA-m98w-cqp3-qcqr

• Source repositories:

  • github.com/gofiber/fiber
  • github.com/gofiber/utils

Credits / Reporter

Reported by @sixcolors (Fiber Maintainer / Security Team)

Kodem intelligence

1. What is CVE-2025-66630? CVE-2025-66630 is a critical-severity security vulnerability in github.com/gofiber/fiber/v2 (go), affecting versions < 2.52.11. It is fixed in 2.52.11.
2. Which versions of github.com/gofiber/fiber/v2 are affected by CVE-2025-66630? github.com/gofiber/fiber/v2 (go) versions < 2.52.11 is affected.
3. Is there a fix for CVE-2025-66630? Yes. CVE-2025-66630 is fixed in 2.52.11. Upgrade to this version or later.
4. Is CVE-2025-66630 exploitable, and should I be worried? Whether CVE-2025-66630 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
5. What actually determines whether CVE-2025-66630 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
6. How do I fix CVE-2025-66630? Upgrade github.com/gofiber/fiber/v2 to 2.52.11 or later.