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When Host is not valid per RFC 3986, the behavior of Hostname and Port was wildly unpredictable, to the point that Host could have a suffix that didn't appear in neither Hostname nor Port. This is a security issue when applications are applying checks to Host and expecting them to be meaningful for the contents of Hostname. To reduce disruption, this change only aims to guarantee the following two security-relevant invariants. * Host is either Hostname or [Hostname] with Port empty, or Hostname:Port or [Hostname]:Port. * Port is only decimals. The second invariant is the one that's most likely to cause disruption, but I believe it's important, as it's conceivable an application might do a suffix check on Host and expect it to be meaningful for the contents of Hostname (if the suffix is not a valid port). There are three ways to ensure it. 1) Reject invalid ports in Parse. Note that non-numeric ports are already rejected if and only if the host starts with "[". 2) Consider non-numeric ports as part of Hostname, not Port. 3) Allow non-numeric ports, and hope they only flow down to net/http, which will reject them (#14353). This change adopts both 1 and 2. We could do only the latter, but then these invalid hosts would flow past port checks, like in http_test.TestTransportRejectsAlphaPort. Non-numeric ports weren't fully supported anyway, because they were rejected after IPv6 literals, so this restores consistency. We could do only the former, but at this point 2) is free and might help with manually constructed Host values (or if we get something wrong in Parse). Note that net.SplitHostPort and net.Dial explicitly accept service names in place of port numbers, but this is an URL package, and RFC 3986, Section 3.2.3, clearly specifies ports as a number in decimal. net/http uses a mix of net.SplitHostPort and url.Parse that would deserve looking into, but in general it seems that it will still accept service names in Addr fields as they are passed to net.Listen, while rejecting them in URLs, which feels correct. This leaves a number of invalid URLs to reject, which however are not security relevant once the two invariants above hold, so can be done in Go 1.14: IPv6 literals without brackets (#31024), invalid IPv6 literals, hostnames with invalid characters, and more. Tested with 200M executions of go-fuzz and the following Fuzz function. u, err := url.Parse(string(data)) if err != nil { return 0 } h := u.Hostname() p := u.Port() switch u.Host { case h + ":" + p: return 1 case "[" + h + "]:" + p: return 1 case h: fallthrough case "[" + h + "]": if p != "" { panic("unexpected Port()") } return 1 } panic("Host is not a variant of [Hostname]:Port") Fixes CVE-2019-14809 Updates #29098 Change-Id: I7ef40823dab28f29511329fa2d5a7fb10c3ec895 Reviewed-on: https://go-review.googlesource.com/c/go/+/189258 Reviewed-by: Ian Lance Taylor <iant@golang.org> |
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