squid -- possible cache-poisoning via malformed HTTP responses

The squid patches page notes:

This patch makes Squid considerably stricter while parsing the HTTP protocol.

1. A Content-length header should only appear once in a valid request or response. Multiple Content-length headers, in conjunction with specially crafted requests, may allow Squid's cache to be poisoned with bad content in certain situations.
2. CR characters is only allowed as part of the CR NL line terminator, not alone. This to ensure that all involved agrees on the structure of HTTP headers.
3. Rejects requests/responses that have whitespace in an HTTP header name.

[source]

To enable these strict parsing rules, update to at least squid-2.5.7_9 and specify relaxed_header_parser off in squid.conf.