Critical UUID Flaw in Fiber v2 on Go 1.24+ Enables Session Hijacking, CSRF Bypass, and Zero-ID DoS Risk

A severe vulnerability has been discovered in Fiber v2, a popular Go web framework, that could allow attackers to hijack user sessions, bypass security protections, and cause service disruptions.

The flaw affects all Fiber v2 versions running on Go 1.23 or earlier and was reported by the framework maintainer six days ago.

The vulnerability lies in Fiber v2’s UUID generation functions, which are used throughout the framework to create unique identifiers for sessions, CSRF tokens, and other security-critical components.

When the system’s random number generator fails to provide secure randomness, a rare but possible scenario, these functions silently fall back to generating a predictable “zero UUID” (00000000-0000-0000-0000-000000000000) instead of alerting developers to the problem.

This silent failure is particularly dangerous because developers have no way of knowing their security tokens have become predictable.

Attribute	Details
CVE ID	CVE-2025-66630
CVSS v4.0	9.2 (AV:N/AC:H/PR:N/UI:N)
CWE	CWE-338 (Weak PRNG)
Affected Versions	< 2.52.11 (Go 1.23 or earlier)
Impact	Predictable UUID fallback to zero UUID

The issue primarily affects users running Go versions before 1.24, as newer versions handle random failures differently, either blocking or panicking rather than returning errors.

Real-World Attack Scenarios

The predictable UUID generation creates multiple security risks. Attackers could predict session identifiers, allowing them to impersonate legitimate users without stealing credentials.

CSRF protection mechanisms that rely on these UUIDs become ineffective, leaving cross-site request forgery attacks unimpeded.

Authentication tokens become guessable, potentially granting unauthorized access to protected resources.

Perhaps most concerning is the denial-of-service risk: when multiple users receive the same zero UUID, session stores and rate limiters collapse into a single shared key, causing data overwrites and system instability.

While modern Linux systems rarely experience random failures, certain environments face a higher risk.

Containerized applications, sandboxed processes, embedded devices, and misconfigured systems lacking proper access to randomness sources (/dev/urandom) are more susceptible.

Sandboxed environments and systems with restricted security policies may also trigger the vulnerability.

According to a the security advisory published, Fiber version 2.52.11 has been released to remediate the critical vulnerability.

Organizations using Fiber v2 should immediately upgrade to this patched version. The fix has been assigned CVE-2025-66630 and carries a “Critical” severity rating with a CVSS score of 8.7 out of 10.

System administrators should also verify that their environments have proper access to secure randomness sources. Review logs for any suspicious patterns of identical session identifiers that might indicate exploitation attempts.

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