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CVE-2026-113603

Status: ReceivedMedium (6.9)—
Severity6.9Medium · CVSS 4.0
Exploitation probability—next 30 days
Active exploitationNonot in the CISA catalog
Public exploitNot knownno public code found

The x402 SIWX server extension in @x402/extensions 2.3.1 through 2.28.0, x402 PyPI 2.11.0 through 2.25.0, and Go module 2.16.0 through 2.28.0 contains an authorization bypass vulnerability that allows paying clients to unlock unpaid routes by supplying a mismatched PaymentPayload.resource URL. Attackers can pay for the cheapest SIWX-protected route while setting resource.url to an expensive route, then repeatedly access it using only a SIGN-IN-WITH-X header without further payment.

CVSS

Base score
6.9
Version
4.0
Vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/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

Exploitation probability (EPSS)

FIRST hasn't scored this CVE yet (usual for very recent or rejected CVEs).

EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).

ATT&CK techniques

How this vulnerability is exploited and what the attacker gains, in MITRE ATT&CK terms.

Vector AV:N/PR:N/UI:N (explotación remota sin autenticación) y CWE-639: el bypass de autorización permite acceder a rutas no pagadas; no hay impacto ATT&CK explícito en el texto.

Inferred by our analysis agent from the official description, CVSS vector and CWE, and checked by a supervisor. May contain errors.

ATT&CK mitigations that cover these techniques

Vulnerability ScanningPrivileged Account ManagementNetwork SegmentationLimit Access to Resource Over NetworkFilter Network TrafficApplication Isolation and Sandboxing

Affected technologies (2)

⚠ AI-inferred from the description — NVD hasn't analyzed this CVE yet, these aren't verified CPEs.

X402 — X402AIX402 — X402 ExtensionsAI

CWEs

References

Show 6 references

Raw JSON (NVD)

Show
{
  "id": "CVE-2026-113603",
  "cveTags": [],
  "metrics": {
    "cvssMetricV31": [
      {
        "type": "Primary",
        "source": "disclosure@vulncheck.com",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 6.5,
          "attackVector": "NETWORK",
          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N",
          "integrityImpact": "LOW",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "NONE",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "LOW"
        },
        "impactScore": 2.5,
        "exploitabilityScore": 3.9
      }
    ],
    "cvssMetricV40": [
      {
        "type": "Secondary",
        "source": "disclosure@vulncheck.com",
        "cvssData": {
          "Safety": "NOT_DEFINED",
          "version": "4.0",
          "Recovery": "NOT_DEFINED",
          "baseScore": 6.9,
          "Automatable": "NOT_DEFINED",
          "attackVector": "NETWORK",
          "baseSeverity": "MEDIUM",
          "valueDensity": "NOT_DEFINED",
          "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/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",
          "exploitMaturity": "NOT_DEFINED",
          "providerUrgency": "NOT_DEFINED",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "attackRequirements": "NONE",
          "privilegesRequired": "NONE",
          "subIntegrityImpact": "NONE",
          "vulnIntegrityImpact": "LOW",
          "integrityRequirement": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
          "subAvailabilityImpact": "NONE",
          "vulnAvailabilityImpact": "NONE",
          "availabilityRequirement": "NOT_DEFINED",
          "modifiedUserInteraction": "NOT_DEFINED",
          "modifiedAttackComplexity": "NOT_DEFINED",
          "subConfidentialityImpact": "NONE",
          "vulnConfidentialityImpact": "LOW",
          "confidentialityRequirement": "NOT_DEFINED",
          "modifiedAttackRequirements": "NOT_DEFINED",
          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedSubIntegrityImpact": "NOT_DEFINED",
          "modifiedVulnIntegrityImpact": "NOT_DEFINED",
          "vulnerabilityResponseEffort": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
          "modifiedVulnConfidentialityImpact": "NOT_DEFINED"
        }
      }
    ]
  },
  "affected": [
    {
      "source": "disclosure@vulncheck.com",
      "affectedData": [
        {
          "repo": "https://github.com/x402-foundation/x402",
          "vendor": "x402-foundation",
          "product": "@x402/extensions",
          "versions": [
            {
              "status": "affected",
              "version": "2.3.1",
              "versionType": "semver",
              "lessThanOrEqual": "2.28.0"
            }
          ],
          "packageURL": "pkg:npm/%40x402/extensions",
          "defaultStatus": "unaffected"
        },
        {
          "repo": "https://github.com/x402-foundation/x402",
          "vendor": "x402-foundation",
          "product": "x402",
          "versions": [
            {
              "status": "affected",
              "version": "2.11.0",
              "versionType": "semver",
              "lessThanOrEqual": "2.25.0"
            }
          ],
          "packageURL": "pkg:pypi/x402",
          "defaultStatus": "unaffected"
        },
        {
          "repo": "https://github.com/x402-foundation/x402",
          "vendor": "x402-foundation",
          "product": "github.com/x402-foundation/x402/go/v2",
          "versions": [
            {
              "status": "affected",
              "version": "2.16.0",
              "versionType": "semver",
              "lessThanOrEqual": "2.28.0"
            }
          ],
          "packageURL": "pkg:golang/github.com/x402-foundation/x402/go/v2",
          "defaultStatus": "unaffected"
        }
      ]
    }
  ],
  "published": "2026-10-20T16:17:10.087",
  "references": [
    {
      "url": "https://github.com/x402-foundation/x402/blob/go/v2.28.0/go/extensions/signinwithx/server.go",
      "source": "disclosure@vulncheck.com"
    },
    {
      "url": "https://github.com/x402-foundation/x402/blob/npm-@x402/extensions@v2.28.0/typescript/packages/extensions/src/sign-in-with-x/hooks.ts",
      "source": "disclosure@vulncheck.com"
    },
    {
      "url": "https://github.com/x402-foundation/x402/blob/pypi-x402@v2.25.0/python/x402/extensions/sign_in_with_x/hooks.py",
      "source": "disclosure@vulncheck.com"
    },
    {
      "url": "https://github.com/x402-foundation/x402/issues/3838",
      "source": "disclosure@vulncheck.com"
    },
    {
      "url": "https://github.com/x402-foundation/x402/pull/3840",
      "source": "disclosure@vulncheck.com"
    },
    {
      "url": "https://www.vulncheck.com/advisories/x402-x402-extensions-2.3.1-through-2.28.0-siwx-payment-bypass-via-paymentpayload-resource",
      "source": "disclosure@vulncheck.com"
    }
  ],
  "vulnStatus": "Received",
  "weaknesses": [
    {
      "type": "Primary",
      "source": "disclosure@vulncheck.com",
      "description": [
        {
          "lang": "en",
          "value": "CWE-639"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "The x402 SIWX server extension in @x402/extensions 2.3.1 through 2.28.0, x402 PyPI 2.11.0 through 2.25.0, and Go module 2.16.0 through 2.28.0 contains an authorization bypass vulnerability that allows paying clients to unlock unpaid routes by supplying a mismatched PaymentPayload.resource URL. Attackers can pay for the cheapest SIWX-protected route while setting resource.url to an expensive route, then repeatedly access it using only a SIGN-IN-WITH-X header without further payment."
    }
  ],
  "lastModified": "2026-10-20T16:17:10.087",
  "sourceIdentifier": "disclosure@vulncheck.com"
}