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CVE-2026-73314 is an improper exceptional-condition handling flaw in XenForo versions before 2.3.13 within the PayPal REST webhook signature-verification logic. Supplying an unsupported authentication-algorithm header value causes algorithm-to-hash mapping to fail; the verification function incorrectly returns a successful result instead of rejecting the request. The webhook handler consequently treats a fabricated payment webhook as signature-verified.
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1 valid exploit after Mallory filtered fakes, detection scripts, and README-only repos.
The repository is a compact Python proof of concept for CVE-2026-73314, accompanied by a README and a Python cache ignore file. poc.py accepts a target URL, a buyer-visible recurring-upgrade request key, amount, and currency. It generates random webhook and transaction identifiers, then POSTs a synthetic PAYMENT.CAPTURE.COMPLETED JSON event to XenForo's PayPal REST callback. The request deliberately declares an unsupported PayPal signature algorithm and includes a non-valid signature. The claimed vulnerable behavior is that XenForo versions before 2.3.13 treat an unavailable/unknown mapped verification algorithm as successful, without fetching a certificate or invoking OpenSSL signature verification. This is an active exploitation PoC, not merely a detector: a successful HTTP 200 response indicates that the callback was accepted. The script has no external C2, persistence, command execution, or additional payload stages.
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6 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A signature-verification logic error in XenForo versions before 2.3.13's PayPal REST webhook handler. An unauthenticated attacker can provide an unsupported auth_algo header value, causing verification to incorrectly succeed and enabling processing of fabricated payment events without a valid PayPal signature.
A remotely exploitable, unauthenticated signature-verification logic flaw in XenForo versions before 2.3.13. An unsupported PayPal REST webhook auth_algo value can cause the verification function to return true, allowing fabricated payment events to be processed without a valid PayPal signature. It is classified as CWE-754 and has CVSS v3.1 vector AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N.
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