Fiber Utils UUIDv4 and UUID Silent Fallback to Predictable Values

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

Fiber Utils is a collection of common functions created for Fiber. In versions 2.0.0-rc.3 and below, when the system's cryptographic random number generator (crypto/rand) fails, both functions silently fall back to returning predictable UUID values, including the zero UUID "00000000-0000-0000-0000-000000000000". The vulnerability occurs through two related but distinct failure paths, both ultimately caused by crypto/rand.Read() failures, compromising the security of all Fiber applications using these functions for security-critical operations. This issue is fixed in version 2.0.0-rc.4.

Source published

9 Dec 2025 01:47:58 UTC

Source modified

9 Dec 2025 16:03:03 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 4.0 · 9.3 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N

Fiber Utils is a collection of common functions created for Fiber. In versions 2.0.0-rc.3 and below, when the system's cryptographic random number generator (crypto/rand) fails, both functions silently fall back to returning predictable UUID values, including the zero UUID "00000000-0000-0000-0000-000000000000". The vulnerability occurs through two related but distinct failure paths, both ultimately caused by crypto/rand.Read() failures, compromising the security of all Fiber applications using these functions for security-critical operations. This issue is fixed in version 2.0.0-rc.4.

Source published

Dec 9, 2025, 1:47:58 AM (timezone not stated)

Source modified

Dec 9, 2025, 4:03:03 PM (timezone not stated)

Observed here

11 Nov 2026 04:33:46 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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EUVD CVSS 4.0 · 9.3 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N

Fiber Utils is a collection of common functions created for Fiber. In versions 2.0.0-rc.3 and below, when the system's cryptographic random number generator (crypto/rand) fails, both functions silently fall back to returning predictable UUID values, including the zero UUID "00000000-0000-0000-0000-000000000000". The vulnerability occurs through two related but distinct failure paths, both ultimately caused by crypto/rand.Read() failures, compromising the security of all Fiber applications using these functions for security-critical operations. This issue is fixed in version 2.0.0-rc.4.

Source published

9 Dec 2025 16:18:21 UTC

Source modified

7 Oct 2026 20:10:01 UTC

Observed here

25 Oct 2026 03:17:36 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · [email protected] · Secondary · 9.3 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

CVSS 3.1 · [email protected] · Primary · 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

## Summary Critical security vulnerabilities exist in both the `UUIDv4()` and `UUID()` functions of the `github.com/gofiber/utils` package. When the system's cryptographic random number generator (`crypto/rand`) fails, both functions silently fall back to returning predictable UUID values, the zero UUID `"00000000-0000-0000-0000-000000000000"`. This compromises the security of all Fiber applications using these functions for security-critical operations on **Go versions prior to 1.24**. **Both functions are vulnerable to the same root cause (`crypto/rand` failure):** * `UUIDv4()`: Indirect vulnerability through `uuid.NewRandom()` → `crypto/rand.Read()` → fallback to `UUID()` * `UUID()`: Direct vulnerability through `crypto/rand.Read(uuidSeed[:])` → silent zero UUID return > **Note:** Go 1.24 and later panics on `crypto/rand` `Read()` failures, mitigating this vulnerability. Applications running on Go 1.24+ are not affected by the silent fallback behavior. --- ## Vulnerability Details ### Affected Functions * **Package**: `github.com/gofiber/utils` * **Functions**: `UUIDv4()` and `UUID()` * **Return Type**: `string` (both functions) * **Locations**: `common.go:93-99` (UUIDv4), `common.go:60-89` (UUID) ### Technical Description The vulnerability occurs through two related but distinct failure paths, both ultimately caused by `crypto/rand.Read()` failures on Go < 1.24: #### Primary Path: UUIDv4() Vulnerability 1. `UUIDv4()` calls `google/uuid.NewRandom()` which internally uses `crypto/rand.Read()` 2. If `uuid.NewRandom()` fails, `UUIDv4()` falls back to the internal `UUID()` function 3. **No error is returned to the application** - silent security failure occurs #### Secondary Path: UUID() Vulnerability 1. `UUID()` directly calls `crypto/rand.Read(uuidSeed[:])` to seed its internal state 2. If seeding fails, `UUID()` **silently fails** and returns the zero UUID `"00000000-0000-0000-0000-000000000000"` 3. Applications receive predictable UUIDs with no indication of the security failure --- ### Code Analysis #### UUIDv4() Vulnerability Path ```go func UUIDv4() string { token, err := uuid.NewRandom() // Uses crypto/rand.Read() internally if err != nil { return UUID() // Dangerous fallback - no error returned to application } return token.String() } ``` #### UUID() Vulnerability Path ```go func UUID() string { uuidSetup.Do(func() { if _, err := rand.Read(uuidSeed[:]); err != nil { // Direct crypto/rand.Read() call return // Silent failure - no seeding, uuidCounter remains 0 } uuidCounter = binary.LittleEndian.Uint64(uuidSeed[:8]) }) if atomic.LoadUint64(&uuidCounter) <= 0 { return "00000000-0000-0000-0000-000000000000" // Zero UUID returned silently } // ... generate UUID from counter } ``` **Root Cause:** Both vulnerabilities stem from `crypto/rand.Read()` failures, occurring through different code paths with the same dangerous silent fallback behavior. --- ## Security Impact ### Severity: CRITICAL This issue is especially severe because many Fiber middleware packages (session, CSRF, auth, rate-limit, request-ID, etc.) default to `utils.UUIDv4()` for generating security-sensitive identifiers. A failure in `crypto/rand` would cause **every generated identifier across the entire application** to collapse to a single predictable value (the zero UUID), resulting in: * **Session fixation / universal session hijack** * **CSRF token predictability and bypass** * **Authentication token replay** * **Global identifier collisions leading to severe application breakage** * **Potential application-wide DoS** due to every request using the same “unique” key, causing cache overwrites, session stomping, corrupted internal maps, and loss of isolation across all users --- ### Attack Scenario While **entropy exhaustion is extremely rare on modern Linux systems**, *RNG access failures* (e.g., restricted `/dev/random` or `/dev/urandom` access, broken container environments, sandbox restrictions, misconfigured VMs, or FIPS-mode RNG failures) are realistic. In these scenarios on **Go < 1.24**, `crypto/rand` may return errors immediately — triggering the vulnerable fallback paths. On **Go 1.24+**, `crypto/rand` `Read()` panics on failure, mitigating the silent-zero fallback issue. --- ### Proof of Concept 1. `uuid.NewRandom()` fails (indirect `crypto/rand.Read()` failure) 2. `UUIDv4()` calls `UUID()` as fallback with no error returned 3. `UUID()` seeding fails directly via `crypto/rand.Read(uuidSeed[:])` 4. Zero UUID `"00000000-0000-0000-0000-000000000000"` is returned silently 5. No error is propagated to the application from either function --- ## Affected Versions * All versions of `github.com/gofiber/utils` containing the `UUIDv4()` or `UUID()` functions * Applications using Fiber middleware that depend on `UUIDv4()` or `UUID` for security * **Only applicable to Go < 1.24**; Go 1.24+ panics/block on `crypto/rand` `Read()` failures and is not affected --- ## Mitigation ### Immediate Workaround Replace usage of `utils.UUIDv4()` with `uuid.New()` or wait for fix: ```go sessionID := uuid.New() ``` ### Recommended Fix Modify `utils.UUIDv4()` and `utils.UUID()` to fail explicitly when cryptographic randomness is unavailable: ```go func UUIDv4() string { token, err := uuid.NewRandom() if err != nil { panic(fmt.Sprintf("utils: failed to generate secure UUID: %v", err)) } return token.String() } func UUID() string { uuidSetup.Do(func() { if _, err := rand.Read(uuidSeed[:]); err != nil { panic(fmt.Sprintf("utils: failed to seed UUID generator: %v", err)) } uuidCounter = binary.LittleEndian.Uint64(uuidSeed[:8]) }) if atomic.LoadUint64(&uuidCounter) <= 0 { panic("utils: UUID generator not properly seeded") } // ... generate UUID from counter } ``` --- ## Detection Applications can detect if they're affected by: 1. Checking if they use `github.com/gofiber/utils` 2. Searching for `UUIDv4()` and `UUID()` usage in security-critical code paths 3. Reviewing Fiber middleware configurations that rely on defaults of `UUIDv4()` for security identifiers --- ## References * **Package Repository**: [https://github.com/gofiber/utils](https://github.com/gofiber/utils) * **Fiber Framework**: [https://github.com/gofiber/fiber](https://github.com/gofiber/fiber) * **Google UUID Library**: [https://github.com/google/uuid](https://github.com/google/uuid) * Golang `crypto/rand` behavior changes: [golang/go#66821](https://github.com/golang/go/issues/66821), [Go 1.25.5 source](https://cs.opensource.google/go/go/+/refs/tags/go1.25.5:src/crypto/rand/rand.go;l=80) --- ## Contact Reported by: [@sixcolors](https://github.com/sixcolors) --- ## Classification * **OWASP**: A02:2021 - Cryptographic Failures * **Impact**: Complete compromise of application security model on Go < 1.24 * **Exploitability**: Medium (requires entropy failure) * **Scope**: All Fiber applications using affected middleware on Go < 1.24

Source published

8 Dec 2025 17:57:26 UTC

Source modified

15 Dec 2025 19:56:09 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V4 · CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N

Publisher rating · CRITICAL

Fiber Utils UUIDv4 and UUID Silent Fallback to Predictable Values in github.com/gofiber/utils

Source published

15 Dec 2025 19:37:35 UTC

Source modified

3 Mar 2026 04:57:45 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.