CVE-2025-66630 Overview
CVE-2025-66630 is an Insecure Random Number Generation vulnerability in Fiber, a popular Express-inspired web framework written in Go. Before version 2.52.11, on Go versions prior to 1.24, the underlying crypto/rand implementation can return an error if secure randomness cannot be obtained. 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 vulnerability is particularly impactful because many Fiber v2 middleware components—including session middleware, CSRF protection, rate limiting, and request-ID generation—default to using the utils.UUIDv4() function. When the underlying crypto/rand fails silently, these security-critical components may operate with predictable identifiers, potentially enabling session hijacking, CSRF bypass, or rate limit circumvention.
Critical Impact
Applications using Fiber v2 before 2.52.11 on Go versions prior to 1.24 may generate predictable UUIDs in security-critical middleware components, potentially enabling session hijacking, CSRF bypass, and authentication attacks.
Affected Products
- Fiber Go Web Framework versions prior to 2.52.11
- Applications running on Go versions prior to 1.24
- Middleware components using utils.UUIDv4() (session, CSRF, rate limiting, request-ID)
Discovery Timeline
- 2026-02-09 - CVE CVE-2025-66630 published to NVD
- 2026-02-09 - Last updated in NVD database
Technical Details for CVE-2025-66630
Vulnerability Analysis
This vulnerability (classified as CWE-338: Use of Cryptographically Weak Pseudo-Random Number Generator) stems from improper error handling in UUID generation routines within the Fiber v2 framework. When the Go runtime's crypto/rand implementation encounters conditions where secure randomness cannot be obtained—such as system entropy exhaustion or certain containerized environments—it returns an error along with potentially predictable data.
The Fiber v2 utils.UUIDv4() function fails to check for or propagate this error condition, causing it to silently return UUIDs generated from non-cryptographic sources. This creates a scenario where applications believe they are using cryptographically secure random identifiers when they may actually be using predictable values.
The impact is amplified by the framework's architecture, where multiple security-critical middleware components rely on this single UUID generation function as their default identifier source.
Root Cause
The root cause is the failure to handle errors returned by Go's crypto/rand.Read() function. In Go versions prior to 1.24, this function can fail under certain conditions (such as system entropy pool exhaustion), returning an error and potentially falling back to less secure randomness sources. The Fiber v2 UUID utility functions did not check for this error condition, causing them to silently proceed with potentially predictable random data.
This design flaw violates the principle of secure defaults, as applications using Fiber middleware would have no indication that their security tokens were compromised.
Attack Vector
An attacker could exploit this vulnerability through the following attack patterns:
Session Hijacking: By predicting session identifiers generated during low-entropy conditions, an attacker could hijack authenticated user sessions without requiring credentials.
CSRF Token Prediction: The CSRF middleware's reliance on predictable UUIDs could allow attackers to craft valid CSRF tokens, bypassing cross-site request forgery protections entirely.
Rate Limit Bypass: Predictable request IDs could enable attackers to circumvent rate limiting by anticipating and manipulating the identifiers used for tracking.
Replay Attacks: Low-entropy UUIDs in request-ID generation could facilitate replay attacks if the same identifiers are reused across multiple requests.
The network-based attack vector with no required privileges makes this vulnerability accessible to remote attackers who can trigger conditions that exhaust system entropy or simply wait for naturally occurring low-entropy states.
Detection Methods for CVE-2025-66630
Indicators of Compromise
- Duplicate or repeated session tokens appearing in application logs
- CSRF validation failures followed by successful bypass attempts
- Unusual patterns of session identifier collisions in database records
- Spike in rate limiting inconsistencies or bypasses
Detection Strategies
- Monitor application logs for duplicate UUID generation or session identifier collisions
- Implement anomaly detection for session fixation patterns or unusual authentication sequences
- Review Go runtime version and Fiber framework version across all deployed applications
- Audit middleware configuration to identify components using default UUID generation
Monitoring Recommendations
- Enable verbose logging on session and CSRF middleware to detect predictable token patterns
- Configure alerts for unusual rates of authentication or session-related events
- Implement entropy monitoring on systems running Fiber applications, particularly in containerized environments
- Deploy application security monitoring to detect session hijacking attempts
How to Mitigate CVE-2025-66630
Immediate Actions Required
- Upgrade Fiber framework to version 2.52.11 or later immediately
- Update Go runtime to version 1.24 or later where possible
- Audit all applications using Fiber v2 to identify affected deployments
- Invalidate all existing sessions and CSRF tokens after patching to eliminate potentially compromised identifiers
Patch Information
The vulnerability is fixed in Fiber version 2.52.11. The fix implements proper error handling for the crypto/rand calls within UUID generation functions, ensuring that errors are either propagated to calling code or handled in a way that prevents the use of predictable random values.
For detailed patch information, refer to the following resources:
Workarounds
- If immediate upgrade is not possible, implement custom UUID generation with explicit error handling using crypto/rand.Read() directly
- Upgrade to Go 1.24 or later, which includes improvements to the crypto/rand implementation that address some underlying issues
- Consider implementing additional entropy sources or monitoring to detect low-entropy conditions
- Deploy rate limiting and anomaly detection at the network edge to mitigate potential exploitation attempts
# Upgrade Fiber to patched version
go get github.com/gofiber/fiber/v2@v2.52.11
# Verify installed version
go list -m github.com/gofiber/fiber/v2
# Update Go runtime to 1.24+ (recommended)
go install golang.org/dl/go1.24@latest
go1.24 download
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
