CVE-2026-73314
XenForo < 2.3.13 Signature Verification Bypass via PayPal REST Webhook
- State
- Published
- Severity
- 8.7 High
- Published
- Sep 8, 2026
- Updated
- Oct 1, 2026
- Reserved
- Aug 11, 2026
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 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 | VulnCheck |
| 3.1 | 7.5 High | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N | VulnCheck |
Weaknesses
- CWE-754 Improper Check for Unusual or Exceptional Conditions
Affected Products
| Product | Versions |
|---|---|
XenForoXenForo |
|
References
- Vendor Advisoryvendor-advisorypatch
- Release Notesrelease-notes
- Researcher Advisorytechnical-description
- Researcher PoCexploit
- https://www.vulncheck.com/advisories/xenforo-signature-verification-bypass-via-paypal-rest-webhookthird-party-advisory
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