CVE-2026-73314
XenForo < 2.3.13 Signature Verification Bypass via PayPal REST Webhook
HIGH 8.7EPSS 0.7%
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.
- Affected
- XenForo
- CVSS v4.0 VULNCHECK
- 8.7 HIGH
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 - CVSS v3.1 VULNCHECK
- 7.5 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N - EPSS
- 0.65% chance of exploitation in the next 30 days, 50th percentile
- Published
- 2026-09-08
- Updated
- 2026-10-01
Proof-of-concept exploits (1)
- BomboBombone/CVE-2026-733140★ · 2026-09-08
Security advisories
- https://bombobombone.github.io/posts/cve-2026-73314
- https://www.vulncheck.com/advisories/xenforo-signature-verification-bypass-via-paypal-res…
- https://xenforo.com/community/threads/security-fixes-released-for-all-xenforo-and-media-g…
- https://xenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-securi…