Vulnerability in Xenforo
CVE-2026-73314
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N.
EPSS exploit prediction
EPSS: 0.007 (50.6th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 51st percentile — 50.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.007 · newest: 0.007 · change: 0.000
Affected products
Weakness classification (CWE)
Public proof-of-concept exploits
References
- Vendor Advisory (vendor-advisory, patch, Release Notes)
- Release Notes (release-notes, Release Notes)
- www.vulncheck.com/advisories/xenforo-signature-verification-bypass-via-paypal-r… (Third Party Advisory, third-party-advisory)
- Researcher Advisory (Exploit, technical-description, Third Party Advisory)
- Researcher PoC (Exploit, exploit, Third Party Advisory)
Frequently asked questions
- What is CVE-2026-73314?
- CVE-2026-73314 is a high-severity vulnerability in Xenforo, classified under Improper Check for Unusual or Exceptional Conditions. CVSS score: 7.5/10. Published 2026-09-08.
- How severe is CVE-2026-73314?
- High severity. CVSS v3 base score is 7.5 out of 10.
- Is CVE-2026-73314 known to be exploited?
- 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.