Joomla! 1.5.x, 2.x, and 3.x before 3.4.6 allow remote attackers to conduct PHP object injection attacks and execute arbitrary PHP code via the HTTP User-Agent header, as exploited in the wild in December 2015.

References

• https://nvd.nist.gov/vuln/detail/CVE-2015-8562
• https://blog.sucuri.net/2015/12/remote-command-execution-vulnerability-in-joomla.html
• https://developer.joomla.org/security-centre/630-20151214-core-remote-code-execution-vulnerability.html
• https://www.exploit-db.com/exploits/38977/
• https://www.exploit-db.com/exploits/39033/
• http://packetstormsecurity.com/files/134949/Joomla-HTTP-Header-Unauthenticated-Remote-Code-Execution.html
• http://packetstormsecurity.com/files/135100/Joomla-3.4.5-Object-Injection.html
• http://www.rapid7.com/db/modules/exploit/multi/http/joomla_http_header_rce
• http://www.securityfocus.com/archive/1/537219/100/0/threaded
• http://www.securityfocus.com/bid/79195