CVE-2025-66565 Overview
CVE-2025-66565 affects Fiber Utils, a collection of common helper functions used by applications built on the Fiber web framework for Go. In versions 2.0.0-rc.3 and below, the UUID generation functions silently fall back to predictable values when the Go cryptographic random number generator (crypto/rand) fails. The fallback can return the zero UUID 00000000-0000-0000-0000-000000000000, undermining any security control that relies on UUID unpredictability. The issue is tracked under [CWE-252: Unchecked Return Value] and is fixed in version 2.0.0-rc.4.
Critical Impact
Applications using Fiber Utils UUID functions for session identifiers, CSRF tokens, or other security-sensitive identifiers may issue predictable or duplicate values, enabling impersonation and authentication bypass.
Affected Products
- Gofiber Utils 2.0.0-beta1 through 2.0.0-beta14
- Gofiber Utils 2.0.0-rc1, rc2, and rc3
- All Fiber applications consuming the affected UUID helper functions
Discovery Timeline
- 2025-12-09 - CVE-2025-66565 published to the National Vulnerability Database
- 2025-12-11 - Last updated in NVD database
Technical Details for CVE-2025-66565
Vulnerability Analysis
The vulnerability resides in two related UUID generation functions exported by the gofiber/utils module. Both functions call crypto/rand.Read() to obtain entropy for UUID construction. When crypto/rand.Read() returns an error, the functions ignore the failure and continue execution using uninitialized or zeroed buffers. The result is a deterministic UUID, including the all-zero UUID, returned to callers that expect a cryptographically unique value.
This is a classic unchecked return value defect mapped to [CWE-252]. The functions do not surface the entropy failure to the caller, and they do not panic or retry. Downstream code treats the returned identifier as random and may use it for session tokens, request correlation IDs, password reset tokens, or CSRF protection. An attacker who can predict or guess these identifiers can hijack sessions, replay requests, or bypass authorization checks tied to UUID-based references.
Root Cause
The root cause is the omission of error handling around crypto/rand.Read() combined with a silent fallback path. Go's crypto/rand.Read() can fail in constrained environments, exhausted entropy pools on certain platforms, or sandboxed containers where /dev/urandom or the platform RNG syscall is unavailable. Without an explicit error check, the function returns a UUID derived from a zero or partially populated byte slice.
Attack Vector
Exploitation requires the target application to encounter a crypto/rand failure while generating a UUID through the affected helpers. An attacker who can induce or observe such failures, or who simply collects issued UUIDs at scale, can identify predictable values such as the zero UUID. The attacker then submits crafted requests using those predictable identifiers to gain unauthorized access to resources protected by UUID-based references. The vulnerability is network-reachable in any Fiber application that exposes endpoints relying on these UUIDs.
No public proof-of-concept exploit is available, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog. The EPSS probability is 0.067%.
Detection Methods for CVE-2025-66565
Indicators of Compromise
- Occurrence of the zero UUID 00000000-0000-0000-0000-000000000000 in session stores, audit logs, or database identifier columns
- Multiple distinct user sessions or records sharing the same UUID value
- Application logs showing entropy or crypto/rand errors without corresponding request failures
- Unexpected access patterns where requests succeed using guessed or repeated UUID values
Detection Strategies
- Perform a software composition analysis scan to identify any service importing github.com/gofiber/utils at a vulnerable version
- Query application data stores for duplicate UUID values or the all-zero UUID across sessions, tokens, and resource identifiers
- Add static analysis rules that flag calls to the affected helper functions in code repositories prior to release
Monitoring Recommendations
- Alert on any log entry containing the zero UUID in authentication, session, or token-issuance pipelines
- Track the frequency of crypto/rand errors emitted by Go runtimes and treat repeated failures as a security event
- Monitor for repeated successful authentication or authorization events that reuse the same UUID across distinct clients
How to Mitigate CVE-2025-66565
Immediate Actions Required
- Upgrade github.com/gofiber/utils to version 2.0.0-rc.4 or later in all Go modules and rebuild affected services
- Invalidate any active sessions, CSRF tokens, password reset links, or API keys that may have been issued by a vulnerable build
- Audit data stores for the zero UUID and other duplicate UUID values, and revoke or regenerate the associated records
Patch Information
The fix is included in Fiber Utils 2.0.0-rc.4. The maintainers committed the change in GitHub commit 6c6cf04, and the disclosure is documented in the GitHub Security Advisory GHSA-m98w-cqp3-qcqr. The patch propagates crypto/rand.Read() errors to callers instead of returning a predictable UUID.
Workarounds
- Replace calls to the vulnerable Fiber Utils UUID helpers with a wrapper that checks the error returned by crypto/rand.Read() and aborts on failure
- Generate UUIDs using a vetted library such as github.com/google/uuid with explicit error handling on entropy failures
- Reject the zero UUID at the application layer as an invalid identifier for sessions, tokens, and resource references
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
