Critical Security Flaw in Fiber v2 on Go 1.23 and Earlier: Immediate Update Required
A significant security vulnerability has been identified in Fiber v2, a widely used web framework for the Go programming language. This flaw poses serious risks, including session hijacking, bypassing of Cross-Site Request Forgery (CSRF) protections, and potential denial-of-service (DoS) attacks. The issue affects all versions of Fiber v2 running on Go 1.23 or earlier.
Understanding the Vulnerability
The core of this vulnerability lies in Fiber v2’s method for generating Universally Unique Identifiers (UUIDs). These identifiers are crucial for maintaining secure sessions, generating CSRF tokens, and other security-related functions within the framework. Under normal circumstances, Fiber v2 relies on the system’s random number generator to produce these UUIDs. However, if the random number generator fails—a rare but possible event—the framework defaults to generating a zero UUID (00000000-0000-0000-0000-000000000000) without notifying the developer.
This silent fallback is particularly dangerous because it renders security tokens predictable. Developers remain unaware that their applications are generating non-unique identifiers, which can be exploited by malicious actors.
Technical Details
– CVE Identifier: CVE-2025-66630
– CVSS v4.0 Score: 9.2 (Critical)
– CWE Classification: CWE-338 (Use of Insufficiently Random Values)
– Affected Versions: Fiber v2 versions prior to 2.52.11 running on Go 1.23 or earlier
– Impact: Predictable UUIDs leading to security vulnerabilities
It’s important to note that this issue primarily affects applications running on Go versions before 1.24. In Go 1.24 and later, the language handles random number generator failures differently, either by blocking operations or triggering a panic, thereby preventing the silent generation of predictable UUIDs.
Potential Attack Scenarios
The implications of this vulnerability are severe:
1. Session Hijacking: Attackers can predict session identifiers, allowing them to impersonate legitimate users without needing to steal credentials.
2. CSRF Protection Bypass: CSRF tokens generated using predictable UUIDs become ineffective, leaving applications vulnerable to cross-site request forgery attacks.
3. Authentication Token Compromise: Predictable authentication tokens can grant unauthorized access to protected resources.
4. Denial-of-Service (DoS) Attacks: Multiple users receiving the same zero UUID can cause session stores and rate limiters to malfunction, leading to data overwrites and system instability.
While modern Linux systems rarely experience random number generator failures, certain environments are more susceptible. These include containerized applications, sandboxed processes, embedded devices, and systems lacking proper access to randomness sources like /dev/urandom. Additionally, sandboxed environments and systems with restricted security policies may inadvertently trigger this vulnerability.
Mitigation and Recommendations
To address this critical issue, the maintainers of Fiber have released version 2.52.11, which includes a fix for the vulnerability. Organizations and developers using Fiber v2 should take the following steps immediately:
1. Upgrade Fiber: Update to Fiber version 2.52.11 or later to incorporate the security patch.
2. Verify Go Version: Ensure that your application is running on Go 1.24 or later to benefit from improved handling of random number generator failures.
3. Audit Security Tokens: Review your application’s logs and security tokens for any instances of the zero UUID, which may indicate prior exploitation or vulnerability.
4. Assess Environment Configuration: Confirm that your deployment environment has proper access to secure randomness sources. This is particularly crucial for containerized or sandboxed applications.
By promptly addressing this vulnerability, developers can safeguard their applications against potential exploits that could compromise user data and system integrity.
