Squid is a caching proxy for the Web. Due to an Improper Validation of Specified Index bug, Squid versions 3.3.0.1 through 5.9 and 6.0 prior to 6.4 compiled using '--with-openssl' are vulnerable to a Denial of Service attack against SSL Certificate validation. This problem allows a remote server to perform Denial of Service against Squid Proxy by initiating a TLS Handshake with a specially crafted SSL Certificate in a server certificate chain. This attack is limited to HTTPS and SSL-Bump. This bug is fixed in Squid version 6.4. In addition, patches addressing this problem for the stable releases can be found in Squid's patch archives. Those who you use a prepackaged version of Squid should refer to the package vendor for availability information on updated packages. Due to chunked decoder lenience Squid is vulnerable to Request/Response smuggling attacks when parsing HTTP/1.1 and ICAP messages. This problem allows a remote client to perform Denial of Service when sending ftp:// URLs in HTTP Request messages or constructing ftp:// URLs from FTP Native input.This issue is triggered during access control security checks, meaning clients may not have been permitted to use the proxy yet.FTP support is always enabled and cannot be disabled completely