From ba872109ef2dc8f1da778651bd1fd3792d0e4587 Mon Sep 17 00:00:00 2001 From: Damien Neil Date: Wed, 10 Jan 2024 13:41:39 -0800 Subject: [PATCH] http2: close connections when receiving too many headers Maintaining HPACK state requires that we parse and process all HEADERS and CONTINUATION frames on a connection. When a request's headers exceed MaxHeaderBytes, we don't allocate memory to store the excess headers but we do parse them. This permits an attacker to cause an HTTP/2 endpoint to read arbitrary amounts of data, all associated with a request which is going to be rejected. Set a limit on the amount of excess header frames we will process before closing a connection. Thanks to Bartek Nowotarski for reporting this issue. Fixes CVE-2023-45288 Fixes golang/go#65051 Change-Id: I15df097268df13bb5a9e9d3a5c04a8a141d850f6 Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/2130527 Reviewed-by: Roland Shoemaker Reviewed-by: Tatiana Bradley Reviewed-on: https://go-review.googlesource.com/c/net/+/576155 Reviewed-by: Dmitri Shuralyov Auto-Submit: Dmitri Shuralyov Reviewed-by: Than McIntosh LUCI-TryBot-Result: Go LUCI --- http2/frame.go | 31 ++++++++++++++++ http2/server_test.go | 84 ++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 115 insertions(+) diff --git a/http2/frame.go b/http2/frame.go index e2b298d85..a5a94411d 100644 --- a/http2/frame.go +++ b/http2/frame.go @@ -1564,6 +1564,7 @@ func (fr *Framer) readMetaFrame(hf *HeadersFrame) (*MetaHeadersFrame, error) { if size > remainSize { hdec.SetEmitEnabled(false) mh.Truncated = true + remainSize = 0 return } remainSize -= size @@ -1576,6 +1577,36 @@ func (fr *Framer) readMetaFrame(hf *HeadersFrame) (*MetaHeadersFrame, error) { var hc headersOrContinuation = hf for { frag := hc.HeaderBlockFragment() + + // Avoid parsing large amounts of headers that we will then discard. + // If the sender exceeds the max header list size by too much, + // skip parsing the fragment and close the connection. + // + // "Too much" is either any CONTINUATION frame after we've already + // exceeded the max header list size (in which case remainSize is 0), + // or a frame whose encoded size is more than twice the remaining + // header list bytes we're willing to accept. + if int64(len(frag)) > int64(2*remainSize) { + if VerboseLogs { + log.Printf("http2: header list too large") + } + // It would be nice to send a RST_STREAM before sending the GOAWAY, + // but the struture of the server's frame writer makes this difficult. + return nil, ConnectionError(ErrCodeProtocol) + } + + // Also close the connection after any CONTINUATION frame following an + // invalid header, since we stop tracking the size of the headers after + // an invalid one. + if invalid != nil { + if VerboseLogs { + log.Printf("http2: invalid header: %v", invalid) + } + // It would be nice to send a RST_STREAM before sending the GOAWAY, + // but the struture of the server's frame writer makes this difficult. + return nil, ConnectionError(ErrCodeProtocol) + } + if _, err := hdec.Write(frag); err != nil { return nil, ConnectionError(ErrCodeCompression) } diff --git a/http2/server_test.go b/http2/server_test.go index afccd9ecd..d400990d2 100644 --- a/http2/server_test.go +++ b/http2/server_test.go @@ -4786,3 +4786,87 @@ Frames: close(s) } } + +func TestServerContinuationFlood(t *testing.T) { + st := newServerTester(t, func(w http.ResponseWriter, r *http.Request) { + fmt.Println(r.Header) + }, func(ts *httptest.Server) { + ts.Config.MaxHeaderBytes = 4096 + }) + defer st.Close() + + st.writePreface() + st.writeInitialSettings() + st.writeSettingsAck() + + st.writeHeaders(HeadersFrameParam{ + StreamID: 1, + BlockFragment: st.encodeHeader(), + EndStream: true, + }) + for i := 0; i < 1000; i++ { + st.fr.WriteContinuation(1, false, st.encodeHeaderRaw( + fmt.Sprintf("x-%v", i), "1234567890", + )) + } + st.fr.WriteContinuation(1, true, st.encodeHeaderRaw( + "x-last-header", "1", + )) + + var sawGoAway bool + for { + f, err := st.readFrame() + if err != nil { + break + } + switch f.(type) { + case *GoAwayFrame: + sawGoAway = true + case *HeadersFrame: + t.Fatalf("received HEADERS frame; want GOAWAY") + } + } + if !sawGoAway { + t.Errorf("connection closed with no GOAWAY frame; want one") + } +} + +func TestServerContinuationAfterInvalidHeader(t *testing.T) { + st := newServerTester(t, func(w http.ResponseWriter, r *http.Request) { + fmt.Println(r.Header) + }) + defer st.Close() + + st.writePreface() + st.writeInitialSettings() + st.writeSettingsAck() + + st.writeHeaders(HeadersFrameParam{ + StreamID: 1, + BlockFragment: st.encodeHeader(), + EndStream: true, + }) + st.fr.WriteContinuation(1, false, st.encodeHeaderRaw( + "x-invalid-header", "\x00", + )) + st.fr.WriteContinuation(1, true, st.encodeHeaderRaw( + "x-valid-header", "1", + )) + + var sawGoAway bool + for { + f, err := st.readFrame() + if err != nil { + break + } + switch f.(type) { + case *GoAwayFrame: + sawGoAway = true + case *HeadersFrame: + t.Fatalf("received HEADERS frame; want GOAWAY") + } + } + if !sawGoAway { + t.Errorf("connection closed with no GOAWAY frame; want one") + } +}