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How the Mentioned CVE Works (CVE-2025-66565)
Fiber Utils provides common functions for the Fiber web framework. The vulnerability exists in its UUID generation functions. When these functions call the system’s secure `crypto/rand.Read()` method, they do not properly handle a failure. If `crypto/rand` fails, the code silently falls back to a predictable, non-random path. This happens through two distinct failure paths within the library’s code. Both paths ultimately lead to the same insecure outcome. Instead of propagating an error or halting, the functions return a deterministic value. This includes the all-zero UUID: “00000000-0000-0000-0000-000000000000”. Any application using these functions for security-critical operations becomes compromised. For example, using these UUIDs for session tokens or unique identifiers is insecure. An attacker who can induce or wait for a `crypto/rand` failure can predict the output. This completely breaks the security assumptions of the UUID. The vulnerability affects all versions from 2.0.0-rc.3 and below. The fix, in version 2.0.0-rc.4, properly handles the random generator failure.
DailyCVE Form
Platform: Fiber Utils
Version: <=2.0.0-rc.3
Vulnerability: Insecure UUID Fallback
Severity: Critical
Date: 2025-12-09
Prediction: Patch released 2025-12-09
What Undercode Say
Analytics
Check if your project uses a vulnerable version npm list @fiber-fns/utils Simulate the insecure fallback (example logic) if crypto_rand_fails: return "00000000-0000-0000-0000-000000000000" Verify the fix in rc.4 grep -n "crypto/rand" node_modules/@fiber-fns/utils/dist/index.js
How Exploit
An attacker exploits this by forcing or anticipating a failure in the system’s cryptographic random number generator. Once the fallback is triggered, the attacker knows the generated “random” UUID will be predictable, such as the zero UUID. This allows them to forge session tokens, bypass authentication checks, or hijack user resources that were thought to be securely protected by an unguessable UUID.
Protection from this CVE
Upgrade immediately to version 2.0.0-rc.4 or later of the `@fiber-fns/utils` package. Review application code to ensure UUIDs from this library are not used for high-security purposes without additional validation. Implement monitoring for cryptographic failures in production systems. Do not rely solely on library-generated UUIDs for secrets; use dedicated secrets management.
Impact
The impact is critical. Security mechanisms relying on the unpredictability of these UUIDs are broken. This can lead to authentication bypass, session hijacking, data integrity violations, and privilege escalation. All applications using the affected functions for generating security tokens, unique file names, or any secure identifier are vulnerable until patched.
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Sources:
Reported By: nvd.nist.gov
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