Quick answers
- Is CVE-2026-67399 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-67399 being exploited in the wild.
- How severe is CVE-2026-67399?
- Informational severity, with a CVSS score of 9.8, published 14 September 2026.
- Which products and versions are affected?
- WHMCS 8.0.0 before 8.13.7, 9.0.0 before 9.0.8.
- Is there a fix for CVE-2026-67399?
- A patch was published on 2026-09-03: Fixes available in WHMCS 9.0.8 and 8.13.7 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-67399 attacked?
- It is attacked over the network, in a web application.
- Am I affected by CVE-2026-67399?
- Check whether you run WHMCS at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
The vulnerability is a PHP deserialization flaw in WHMCS 8.0.x and later versions that fails to properly validate or restrict forged payloads before processing them. An unauthenticated remote attacker can craft malicious serialized objects and submit them to a vulnerable endpoint, triggering unsafe deserialization that leads to arbitrary code execution with server privileges. The attack requires no prior authentication or user interaction. The flaw affects all 9.x versions before 9.0.8 and all 8.x versions before 8.13.7; patches are available in WHMCS 9.0.8 and 8.13.7 respectively.
Affected products
- WHMCS WHMCS 8.0.0 before 8.13.7, 9.0.0 before 9.0.8
Timeline
- 2026-09-03: disclosed: WHMCS published security advisory
- 2026-09-03: patched: Fixes available in WHMCS 9.0.8 and 8.13.7
- 2026-09-14: advisory: CVE-2026-67399 published on NVD