Critical Zero-Day Pre-authentication Remote Code Execution Exploit Published for 5.x Versions of vBulletin

Ryan Seguin

New critical zero-day pre-auth RCE exploit code published on Full Disclosure mailing list for 5.x versions of vBulletin (CVE-2019-16759).

UPDATE 09/25/2019: The background and solution sections below have been updated to reflect the security patch issued by the vBulletin team.

Background

A preauthentication remote code execution (RCE) zero-day exploit was recently disclosed anonymously for vBulletin 5.x. This zero-day does not seem to have followed coordinated disclosure procedures. VBulletin released a new security patch for vBulletin versions 5.5.2, 5.5.3, and 5.5.4.

Analysis

Tenable Research has analyzed and confirmed that this exploit works on default configurations of vBulletin. Based on the public PoC, an unauthenticated attacker can send a specially crafted HTTP POST request to a vulnerable vBulletin host and execute commands. These commands would be executed with the permissions of the user account that the vBulletin service is utilizing. Depending on the service user’s permissions, this could allow complete control of a host.

Proof of concept

The published exploit code returns its successful execution in a JSON formatted response.

Solution

The vBulletin team has issued a patch for CVE-2019-16759 for vBulletin versions 5.5.2, 5.5.3, and 5.5.4. Users on earlier versions of vBulletin 5.x will need to update to one of the currently supported versions in order to apply the patch. VBulletin cloud users don’t need to perform any additional actions as the fix has already been applied to the cloud version.

Identifying affected systems

A list of Tenable plugins to identify this vulnerability will appear here as they’re released.

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Published on Sep 24, 2019

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