EUVD-2026-72785
GHSA-rqwm-9m4j-f7g3
Severity by source
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/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
Network-reachable webhook endpoint, no credentials or interaction needed; impact is integrity-only (payment event forgery), no confidentiality or availability effect.
Primary rating from Vendor (VulnCheck).
CVSS VectorVendor: VulnCheck
Lifecycle Timeline
2DescriptionCVE.org
XenForo before 2.3.13 contains a signature verification logic error in the PayPal REST webhook handler that allows unauthenticated attackers to bypass payment signature validation by submitting a webhook request with an unsupported auth_algo header value. When the algorithm cannot be mapped to a supported hash function, the verification function incorrectly returns true instead of failing, causing the caller to treat the fabricated request as verified and process the payment event without a valid PayPal signature.
AnalysisAI
Unauthenticated payment event forgery in XenForo before 2.3.13 stems from a logic error in the PayPal REST webhook signature verification routine: when the incoming auth_algo header value cannot be mapped to a supported hash function, the verification function incorrectly returns true, causing the application to accept fabricated webhook payloads as legitimate PayPal events. Any XenForo installation with PayPal REST payment integration enabled prior to version 2.3.13 is affected. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires that the target XenForo installation has the PayPal REST payment processor enabled and configured (non-default for installations that never set up PayPal payments). … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:N) correctly reflects that the webhook endpoint is network-accessible, requires no credentials, and demands no user interaction, making automated abuse straightforward; even a mid-sized community operator running XenForo in sopot should treat this as urgent if PayPal REST payments are enabled. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | Upgrade to XenForo 2.3.13, the vendor-confirmed patched release per the advisory at https://xenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857/. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, identify all XenForo deployments running versions before 2.3.13 with PayPal REST integration enabled, and quantify financial exposure by reviewing recent transaction volumes. …
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External POC / Exploit Code
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