Platform
php
Component
xenforo
Fixed in
2.3.9
2.2.18
CVE-2026-35056 is a Remote Code Execution (RCE) vulnerability affecting XenForo. This vulnerability allows an authenticated, but malicious, admin user to execute arbitrary code on the server, potentially leading to complete system compromise. This affects XenForo versions 2.3.0 through 2.3.9. The vulnerability is fixed in version 2.3.9.
CVE-2026-35056 in XenForo, affecting versions prior to 2.3.9 and 2.2.18, enables Remote Code Execution (RCE) by authenticated, yet malicious, admin users. This means an administrator with access to the admin panel, but with nefarious intentions, can execute arbitrary code on the server hosting the forum. The impact is severe, as an attacker could gain complete control of the server, compromise sensitive user data, modify forum content, or even use the server as a springboard for attacks on other systems. The vulnerability is exploited by leveraging a flaw in the handling of certain administrative functions, allowing for malicious code injection. The seriousness of the issue lies in the ease with which a malicious administrator can exploit it, without requiring advanced technical skills.
This vulnerability is triggered when a malicious administrator interacts with a specific administrative panel function that hasn't been properly validated. The attacker can inject malicious code through input parameters or by manipulating data that the system processes. The injected code executes with the administrator's privileges, allowing access to any server resources. Exploitation does not require external authentication, as the attacker must be an existing administrator. The complexity of exploitation is relatively low, making it accessible to a wide range of attackers. The lack of adequate user input validation is the primary cause of this vulnerability.
Exploit Status
EPSS
0.43% (62% percentile)
CISA SSVC
The most effective mitigation for CVE-2026-35056 is to update XenForo to version 2.3.9 or higher, or to version 2.2.18 or higher. These versions include a fix that eliminates the vulnerability. It is crucial to perform this update as soon as possible to protect your forum. Additionally, it's recommended to review the permissions of forum administrators and limit access only to those users who genuinely require it. Implementing robust password policies and enabling two-factor authentication (2FA) for administrators can add an extra layer of security. Monitoring server logs for suspicious activity can also help detect and respond to potential attacks.
Update XenForo to version 2.3.9 or 2.2.18, or a later version. This will fix the remote code execution vulnerability for authenticated admin users.
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Versions prior to 2.3.9 and 2.2.18 are vulnerable to this vulnerability.
Check the XenForo version in the admin panel, under the 'Forum Information' section.
If you can't update immediately, consider limiting administrative access and monitoring server logs.
There isn't a specific tool, but you can look for recently modified files or unusual activity in server logs.
The vulnerability was discovered and reported by the XenForo developers.
CVSS Vector
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