CVE-2026-61511 vBulletin CVE debrief

Who should care

Administrators and users of vBulletin 5.x and 6.x versions should be aware of this critical vulnerability. Immediate action is required to prevent potential exploitation. Affected operators and platforms should prioritize patching or mitigating the vulnerability. Vulnerability management and security teams should track the exposure and verify the effectiveness of compensating controls.

Technical summary

The eval injection vulnerability in vBulletin is caused by the vB5_Template_Runtime::runMaths() method not properly sanitizing user input. This allows attackers to inject and execute arbitrary PHP code via the unauthenticated ajax/render template route. The vulnerability has a CVSS score of 9.3 and is considered critical. The insufficiently restrictive regex filter can be exploited by using phpfuck-style encoding with permitted characters.

Defensive priority

High

Recommended defensive actions

• Apply the official patch or upgrade to a non-vulnerable version of vBulletin.
• Restrict access to the ajax/render template route.
• Monitor for suspicious activity and implement additional security measures.
• Review compensating controls for exposed systems while remediation is scheduled and verified.
• Check relevant monitoring, detection, and logs for exposed assets that need extra review.
• Track exceptions, retest remediated assets, and close the item only after evidence is documented.
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.

Evidence notes

The CVE record was published on 2026-07-27T14:16:59.177Z and last modified on 2026-07-27T20:36:13.407Z. The NVD entry is currently Deferred. Evidence is limited, and defenders should verify the affected scope and severity with the vendor. The vulnerability affects vBulletin 5.x through 5.7.5 and 6.x through 6.2.1. The eval injection vulnerability is located in the vB5_Template_Runtime::runMaths() method within the template runtime.

Official resources