Squid, when transparent interception mode is enabled, uses the HTTP Host header to determine the remote endpoint, which allows remote attackers to bypass access controls for Flash, Java, Silverlight, and probably other technologies, and possibly communicate with restricted intranet sites, via a crafted web page that causes a client to send HTTP requests with a modified Host header.

References

• https://nvd.nist.gov/vuln/detail/CVE-2009-0801
• http://www.kb.cert.org/vuls/id/435052
• http://www.securityfocus.com/bid/33858