High-severity vulnerability in vBulletin is being actively exploited

Enlarge (credit: vBulletin)

Attackers are mass-exploiting an anonymously disclosed vulnerability that makes it possible to take control of servers running vBulletin, one of the Internet's most popular applications for website comments. Sites running the app should take comments offline until administrators install a patch that vBulletin developers released late Wednesday morning.

The vulnerability was disclosed through an 18-line exploit that was published on Monday by an unidentified person. The exploit allows unauthenticated attackers to remotely execute malicious code on just about any vBulletin server running versions 5.0.0 up to 5.5.4. The vulnerability is so severe and easy to exploit that some critics have described it as a back door.

"Essentially, any attack exploits a super simple command injection," Ryan Seguin, a research engineer at Tenable, told Ars. "An attacker sends the payload, vBulletin then runs the command, and it responds back to the attacker with whatever they asked for. If an attacker issues a shell command as part of the injection, vBulletin will run Linux commands on its host with whatever user permissions vBulletins' system-level user account has access to." Seguin has more in this technical analysis of the vulnerability.

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