CVE-2025-66565: Gofiber Utils Information Disclosure Flaw

CVE-2025-66565 Overview

CVE-2025-66565 is a critical Insecure Random Number Generation vulnerability affecting Gofiber Utils, a collection of common functions created for the Fiber web framework. In versions 2.0.0-rc.3 and below, when the system's cryptographic random number generator (crypto/rand) fails, both UUID generation functions silently fall back to returning predictable UUID values, including the zero UUID "00000000-0000-0000-0000-000000000000". This vulnerability compromises the security of all Fiber applications using these functions for security-critical operations such as session tokens, CSRF tokens, or unique identifiers.

Critical Impact

Applications using affected versions may generate predictable or zero UUIDs when the cryptographic random number generator fails, potentially allowing attackers to bypass authentication, predict session tokens, or compromise other security-critical operations that rely on UUID uniqueness.

Affected Products

• Gofiber Utils versions prior to 2.0.0-rc.3
• Gofiber Utils 2.0.0-beta1 through 2.0.0-beta14
• Gofiber Utils 2.0.0-rc.1, 2.0.0-rc.2, and 2.0.0-rc.3

Discovery Timeline

• December 9, 2025 - CVE-2025-66565 published to NVD
• December 11, 2025 - Last updated in NVD database

Technical Details for CVE-2025-66565

Vulnerability Analysis

The vulnerability occurs through two related but distinct failure paths, both ultimately caused by crypto/rand.Read() failures. When the UUID generator's setup function encounters an error reading from the cryptographic random source, the vulnerable code silently returns without properly seeding the UUID counter. This results in the counter remaining at zero, causing subsequent UUID generation calls to return the predictable zero UUID value.

The security implications are severe for applications using these UUID functions for security-critical operations. Session identifiers, CSRF tokens, API keys, and other security-sensitive values generated during a crypto/rand failure would all be predictable, enabling attackers to forge sessions or bypass security controls.

Root Cause

The root cause is improper error handling (CWE-252: Unchecked Return Value) in the UUID seeding mechanism. When crypto/rand.Read() fails to properly seed the UUID generator, the code simply returns without raising an error or alerting the application. Additionally, if the uuidCounter is found to be zero (indicating failed initialization), the function returns a hardcoded zero UUID instead of failing safely. This silent failure pattern masks critical security issues from application developers.

Attack Vector

This vulnerability is exploitable over the network without authentication or user interaction. An attacker could exploit this vulnerability by:

1. Identifying applications using affected Gofiber Utils versions for UUID generation
2. Triggering conditions that cause crypto/rand failures (e.g., entropy starvation, resource exhaustion)
3. Predicting or using the zero UUID to bypass security mechanisms
4. Leveraging predictable UUIDs to hijack sessions, forge tokens, or access protected resources

The following patch demonstrates how the vulnerability was addressed by replacing silent failures with explicit panics:

 	// Setup seed & counter once
 	uuidSetup.Do(func() {
 		if _, err := rand.Read(uuidSeed[:]); err != nil {
-			return
+			panic(fmt.Sprintf("utils: failed to seed UUID generator: %v", err))
 		}
 		uuidCounter = binary.LittleEndian.Uint64(uuidSeed[:8])
 	})
 	if atomic.LoadUint64(&uuidCounter) <= 0 {
-		return "00000000-0000-0000-0000-000000000000"
+		panic("utils: UUID generator not properly seeded")
 	}
 	// first 8 bytes differ, taking a slice of the first 16 bytes
 	x := atomic.AddUint64(&uuidCounter, 1)

Source: GitHub Commit 6c6cf04

Detection Methods for CVE-2025-66565

Indicators of Compromise

• Presence of zero UUID values (00000000-0000-0000-0000-000000000000) in session tokens, CSRF tokens, or other security-critical identifiers
• Multiple requests or sessions sharing identical UUID values
• Logs indicating crypto/rand read failures or entropy-related errors
• Unusual patterns of successful authentication with predictable token values

Detection Strategies

• Audit application logs for zero UUID generation or crypto/rand failure messages
• Implement monitoring for session token collision detection across the application
• Use dependency scanning tools to identify affected Gofiber Utils versions in your Go modules
• Review go.mod files for github.com/gofiber/utils dependencies below version 2.0.0-rc.4

Monitoring Recommendations

• Configure alerts for entropy pool depletion on application servers
• Monitor for abnormal patterns of identical session or token values across different users
• Implement runtime detection for predictable UUID patterns in security-critical contexts
• Use SentinelOne Singularity to monitor for exploitation attempts targeting cryptographic weaknesses

How to Mitigate CVE-2025-66565

Immediate Actions Required

• Upgrade Gofiber Utils to version 2.0.0-rc.4 or later immediately
• Audit existing session tokens, CSRF tokens, and other UUID-based security values for predictability
• Invalidate and regenerate all active sessions after upgrading to ensure no compromised tokens remain
• Review application logs for evidence of zero UUID generation during the vulnerable period

Patch Information

The vulnerability has been patched in Gofiber Utils version 2.0.0-rc.4. The fix replaces silent failure behavior with explicit panics when the UUID generator cannot be properly seeded, ensuring applications fail safely rather than operating with predictable values. Review the GitHub Security Advisory GHSA-m98w-cqp3-qcqr for complete details.

Workarounds

• If immediate upgrade is not possible, implement additional validation to reject zero or predictable UUID values in security-critical operations
• Add application-level checks to detect and reject the zero UUID pattern before use
• Consider implementing fallback cryptographic random sources at the application level
• Monitor system entropy levels and ensure adequate randomness sources are available

# Update Gofiber Utils to the patched version
go get github.com/gofiber/utils/v2@v2.0.0-rc.4

# Verify the updated version
go list -m github.com/gofiber/utils/v2

# Run go mod tidy to clean up dependencies
go mod tidy