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

Vulnerability summary

CVE-2025-66565 is a critical (CVSS 9.8) Unchecked Return Value vulnerability in gofiber utils. EPSS estimates a 0.47% chance of exploitation in the next 30 days, higher than 39.5% of scored vulnerabilities.

Timeline

1. 09-12-2025
   PublishedVulnerability first disclosed.
2. 09-12-2025
   Last modifiedVulnerability information updated.

Description

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.

• CWE-252Unchecked Return ValueThe product does not check the return value from a method or function, which can prevent it from detecting unexpected states and conditions.
• CWE-331Insufficient EntropyThe product uses an algorithm or scheme that produces insufficient entropy, leaving patterns or clusters of values that are more likely to occur than others.
• CWE-338Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG)The product uses a Pseudo-Random Number Generator (PRNG) in a security context, but the PRNG's algorithm is not cryptographically strong.