My web app stopped working in apache2 2.4.10-10+deb8u8 and looks like the reason is this:
* CVE-2016-8743: Enforce more HTTP conformance for request lines and request headers, to prevent response splitting and cache pollution by malicious clients or downstream proxies. If this causes problems with non-conforming clients, some checks can be relaxed by adding the new directive 'HttpProtocolOptions unsafe' to the configuration. Differently than the upstream 2.4.25 release which will also be in the Debian 9 (stretch) release, this update for Debian 8 (jessie) accepts underscores in host and domain names even while 'HttpProtocolOptions strict' is in effect. More information is available at http://httpd.apache.org/docs/2.4/mod/core.html#httpprotocoloptions I checked at the referenced RFCs and underscore IS a valid character in a segment (rfc3986): absolute-path = 1*( "/" segment ) segment = *pchar pchar = unreserved / pct-encoded / sub-delims / ":" / "@" unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~" Why is it that if I have _ in my segment, apache2 rejects the request without 'HttpProtocolOptions strict'? -- Juha