Vulnerability · Published Sep 8, 2026 · Assigned by VulnCheck

CVE-2026-73314XenForo < 2.3.13 Signature Verification Bypass via PayPal REST Webhook

High 7.5

In plain English

A high-severity security flaw in XenForo from XenForo. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.7% (higher than 51% of all known vulnerabilities). Ready-made attack tooling exists: public proof-of-concept code.

Severity (CVSS 3.1)7.5High

Exploit odds (30 days)0.7%top 48.6% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack tooling1Public PoC

Official description

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 products (as reported)

Vendor	Product	Versions
XenForo	XenForo	0 – before 2.3.13

Weakness: CWE-754 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

References

Vendor Advisory vendor-advisory, patch
Release Notes release-notes
Researcher Advisory technical-description
Researcher PoC exploit
https://www.vulncheck.com/advisories/xenforo-signature-verification-bypass-via-paypal-rest-webhook third-party-advisory