CVE-2025-66630: Fiber has an insecure fallback in utils.UUIDv4() / utils.UUID() — predictable / zero‑UUID on crypto/rand failure

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 0.5%, percentile 44: FIRST’s model estimates a 0.5% chance of exploitation activity in the next 30 days, higher than 44% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes github.com/gofiber/fiber/v2 (Go) < 2.52.11, fixed in 2.52.11. Check your lockfile, including transitive dependencies.

What it is

Fiber is an Express inspired web framework written in Go. Before 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 is especially impactful because many Fiber v2 middleware components (session middleware, CSRF, rate limiting, request-ID generation, etc.) default to using utils.UUIDv4(). This vulnerability is fixed in 2.52.11.

From the GitHub advisory

Fiber v2 contains an internal vendored copy of gofiber/utils, and its functions UUIDv4() and UUID() inherit the same critical weakness described in the upstream advisory. On Go versions prior to 1.24, the underlying crypto/rand implementation can return an error if secure randomness cannot be obtained. In such cases, these Fiber v2 UUID functions silently fall back to generating predictable values — the all-zero UUID 00000000-0000-0000-0000-000000000000.

On Go 1.24+, the language guarantees that crypto/rand no longer returns an error (it will block or panic instead), so this vulnerability primarily affects Fiber v2 users running Go 1.23 or earlier, which Fiber v2 officially supports.

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 is especially impactful because many Fiber v2 middleware components (session middleware, CSRF, rate limiting, request-ID generation, etc.) default to using utils.UUIDv4().

Impact includes, but is not limited to:

Session fixation or hijacking (predictable session IDs) CSRF token forgery or bypass Authentication replay / token prediction Potential denial-of-service (DoS): if the zero UUID is generated, key-based structures (sessions, rate-limits, caches, CSRF stores) may collapse into a single shared key, causing overwrites, lock contention, or state corruption Request-ID collisions, undermining logging and trace integrity General compromise of confidentiality, integrity, and authorization logic relying on UUIDs for uniqueness or secrecy

Weakness type: CWE-338.

Product: github.com/gofiber/fiber/v2 (Go) · Assigned by: GitHub_M · Published: 2026-02-09

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: high (needs special conditions)
• Attack requirements: none
• Privileges required: none (no login)
• User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation none, automatable no, technical impact partial.
• FIRST EPSS (model of 2026-10-21): 0.53% probability of exploitation activity in the next 30 days; percentile 44.

Timeline

• 2026-02-09 — CVE record published by GitHub_M
• 2026-02-09 — GitHub-reviewed advisory GHSA-68rr-p4fp-j59v published (critical)
• 2026-02-10 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-68rr-p4fp-j59v github.com
2. CVE.org record CVE-2025-66630 cve.org
3. NVD entry CVE-2025-66630 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com

Critical Go advisories · Today’s Security Digest