From 41b1f88efab9d263408448bf139659119002ea50 Mon Sep 17 00:00:00 2001 From: Filippo Valsorda Date: Thu, 12 Sep 2019 12:37:36 -0400 Subject: [PATCH] net/textproto: don't normalize headers with spaces before the colon RFC 7230 is clear about headers with a space before the colon, like X-Answer : 42 being invalid, but we've been accepting and normalizing them for compatibility purposes since CL 5690059 in 2012. On the client side, this is harmless and indeed most browsers behave the same to this day. On the server side, this becomes a security issue when the behavior doesn't match that of a reverse proxy sitting in front of the server. For example, if a WAF accepts them without normalizing them, it might be possible to bypass its filters, because the Go server would interpret the header differently. Worse, if the reverse proxy coalesces requests onto a single HTTP/1.1 connection to a Go server, the understanding of the request boundaries can get out of sync between them, allowing an attacker to tack an arbitrary method and path onto a request by other clients, including authentication headers unknown to the attacker. This was recently presented at multiple security conferences: https://portswigger.net/blog/http-desync-attacks-request-smuggling-reborn net/http servers already reject header keys with invalid characters. Simply stop normalizing extra spaces in net/textproto, let it return them unchanged like it does for other invalid headers, and let net/http enforce RFC 7230, which is HTTP specific. This loses us normalization on the client side, but there's no right answer on the client side anyway, and hiding the issue sounds worse than letting the application decide. Fixes CVE-2019-16276 Fixes #34540 Change-Id: I6d272de827e0870da85d93df770d6a0e161bbcf1 Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/549719 Reviewed-by: Brad Fitzpatrick Reviewed-on: https://go-review.googlesource.com/c/go/+/197503 Run-TryBot: Filippo Valsorda TryBot-Result: Gobot Gobot Reviewed-by: Dmitri Shuralyov --- src/net/http/serve_test.go | 4 ++++ src/net/http/transport_test.go | 27 +++++++++++++++++++++++++++ src/net/textproto/reader.go | 10 ++-------- src/net/textproto/reader_test.go | 13 ++++++------- 4 files changed, 39 insertions(+), 15 deletions(-) diff --git a/src/net/http/serve_test.go b/src/net/http/serve_test.go index 61adda2604..1d1449aa65 100644 --- a/src/net/http/serve_test.go +++ b/src/net/http/serve_test.go @@ -4755,6 +4755,10 @@ func TestServerValidatesHeaders(t *testing.T) { {"foo\xffbar: foo\r\n", 400}, // binary in header {"foo\x00bar: foo\r\n", 400}, // binary in header {"Foo: " + strings.Repeat("x", 1<<21) + "\r\n", 431}, // header too large + // Spaces between the header key and colon are not allowed. + // See RFC 7230, Section 3.2.4. + {"Foo : bar\r\n", 400}, + {"Foo\t: bar\r\n", 400}, {"foo: foo foo\r\n", 200}, // LWS space is okay {"foo: foo\tfoo\r\n", 200}, // LWS tab is okay diff --git a/src/net/http/transport_test.go b/src/net/http/transport_test.go index e94ade5f7f..d7eef0d94c 100644 --- a/src/net/http/transport_test.go +++ b/src/net/http/transport_test.go @@ -5692,3 +5692,30 @@ func TestTransportIgnores408(t *testing.T) { } t.Fatalf("timeout after %v waiting for Transport connections to die off", time.Since(t0)) } + +func TestInvalidHeaderResponse(t *testing.T) { + setParallel(t) + defer afterTest(t) + cst := newClientServerTest(t, h1Mode, HandlerFunc(func(w ResponseWriter, r *Request) { + conn, buf, _ := w.(Hijacker).Hijack() + buf.Write([]byte("HTTP/1.1 200 OK\r\n" + + "Date: Wed, 30 Aug 2017 19:09:27 GMT\r\n" + + "Content-Type: text/html; charset=utf-8\r\n" + + "Content-Length: 0\r\n" + + "Foo : bar\r\n\r\n")) + buf.Flush() + conn.Close() + })) + defer cst.close() + res, err := cst.c.Get(cst.ts.URL) + if err != nil { + t.Fatal(err) + } + defer res.Body.Close() + if v := res.Header.Get("Foo"); v != "" { + t.Errorf(`unexpected "Foo" header: %q`, v) + } + if v := res.Header.Get("Foo "); v != "bar" { + t.Errorf(`bad "Foo " header value: %q, want %q`, v, "bar") + } +} diff --git a/src/net/textproto/reader.go b/src/net/textproto/reader.go index a5cab993b2..87f901b4fc 100644 --- a/src/net/textproto/reader.go +++ b/src/net/textproto/reader.go @@ -495,18 +495,12 @@ func (r *Reader) ReadMIMEHeader() (MIMEHeader, error) { return m, err } - // Key ends at first colon; should not have trailing spaces - // but they appear in the wild, violating specs, so we remove - // them if present. + // Key ends at first colon. i := bytes.IndexByte(kv, ':') if i < 0 { return m, ProtocolError("malformed MIME header line: " + string(kv)) } - endKey := i - for endKey > 0 && kv[endKey-1] == ' ' { - endKey-- - } - key := canonicalMIMEHeaderKey(kv[:endKey]) + key := canonicalMIMEHeaderKey(kv[:i]) // As per RFC 7230 field-name is a token, tokens consist of one or more chars. // We could return a ProtocolError here, but better to be liberal in what we diff --git a/src/net/textproto/reader_test.go b/src/net/textproto/reader_test.go index 6ff7eefe91..97fb1ab028 100644 --- a/src/net/textproto/reader_test.go +++ b/src/net/textproto/reader_test.go @@ -188,11 +188,10 @@ func TestLargeReadMIMEHeader(t *testing.T) { } } -// Test that we read slightly-bogus MIME headers seen in the wild, -// with spaces before colons, and spaces in keys. +// TestReadMIMEHeaderNonCompliant checks that we don't normalize headers +// with spaces before colons, and accept spaces in keys. func TestReadMIMEHeaderNonCompliant(t *testing.T) { - // Invalid HTTP response header as sent by an Axis security - // camera: (this is handled by IE, Firefox, Chrome, curl, etc.) + // These invalid headers will be rejected by net/http according to RFC 7230. r := reader("Foo: bar\r\n" + "Content-Language: en\r\n" + "SID : 0\r\n" + @@ -202,9 +201,9 @@ func TestReadMIMEHeaderNonCompliant(t *testing.T) { want := MIMEHeader{ "Foo": {"bar"}, "Content-Language": {"en"}, - "Sid": {"0"}, - "Audio Mode": {"None"}, - "Privilege": {"127"}, + "SID ": {"0"}, + "Audio Mode ": {"None"}, + "Privilege ": {"127"}, } if !reflect.DeepEqual(m, want) || err != nil { t.Fatalf("ReadMIMEHeader =\n%v, %v; want:\n%v", m, err, want)