CVE-2026-61511 in vBulletin
Summary
by MITRE • 07/27/2026
vBulletin 5.x through 5.7.5 and 6.x through 6.2.1 contains an eval injection vulnerability in the vB5_Template_Runtime::runMaths() method within the template runtime that allows unauthenticated remote attackers to execute arbitrary PHP code by supplying crafted input through the pagenav[pagenumber] parameter. Attackers can exploit the insufficiently restrictive regex filter by using phpfuck-style encoding with permitted characters to inject and execute arbitrary PHP code via the unauthenticated ajax/render template route without any authentication.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 07/27/2026
The vulnerability in vBulletin versions 5.x through 5.7.5 and 6.x through 6.2.1 represents a critical remote code execution flaw classified under CWE-94, which specifically addresses the execution of arbitrary code due to improper input validation. This vulnerability exists within the vB5_Template_Runtime::runMaths() method, where the application fails to properly sanitize user-supplied input before processing mathematical expressions. The flaw manifests when attackers manipulate the pagenav[pagenumber] parameter through the ajax/render template route, exploiting a weakness in the regex filtering mechanism that should have prevented dangerous code injection patterns.
The technical implementation of this vulnerability stems from insufficient input validation and sanitization within the template runtime engine. Attackers can bypass the restrictive regex filter by employing phpfuck-style encoding techniques that utilize permitted characters to construct malicious payloads. This approach allows them to inject arbitrary PHP code that gets executed within the application context without requiring any authentication credentials. The exploitation occurs through an unauthenticated ajax/render template route, which means the vulnerability can be leveraged by anyone with access to the affected web application, making it particularly dangerous for publicly accessible systems.
The operational impact of this vulnerability extends beyond simple code execution, as it enables attackers to perform a wide range of malicious activities including data exfiltration, system compromise, and persistent backdoor installation. The attack surface is significantly broadened by the fact that no authentication is required, meaning any user can trigger the vulnerability. This creates an immediate risk for organizations running affected vBulletin versions, as the attack vector is both accessible and exploitable without specialized knowledge or credentials. The vulnerability directly maps to attack techniques described in the MITRE ATT&CK framework under T1059.007 for PHP code execution and T1190 for exploitation of remote services.
Organizations should implement immediate mitigations including patching to the latest available versions, which contain proper input validation and sanitization measures. Network-level protections such as web application firewalls can provide temporary defense while patches are deployed, though these solutions may not be foolproof against sophisticated variants of the attack. The vulnerability demonstrates a classic example of improper input handling that should be prevented through robust validation mechanisms. Security teams must also consider the broader implications for their incident response procedures and ensure proper monitoring is in place to detect potential exploitation attempts. Additionally, implementing principle of least privilege access controls and regular security assessments can help reduce the overall risk exposure from such vulnerabilities.
The vulnerability serves as a reminder of critical security principles including input validation, output encoding, and secure coding practices that should be enforced throughout the software development lifecycle. Proper implementation of these security measures would have prevented the exploitation path that allows attackers to bypass the intended filtering mechanisms. Organizations should also consider implementing automated vulnerability scanning tools that can detect similar patterns in their codebases and ensure that all third-party components are regularly updated and assessed for known vulnerabilities.