SIPSorcery: Malformed UDP packet on the RTP/ICE socket can remotely terminate a media session (DoS)

Impact

A single malformed inbound UDP packet on the RTP/ICE socket can remotely terminate an active RTP or WebRTC media session. The packet receive handler indexes packet (and STUN attribute) bytes without sufficient length checks and throws, and the UDP receive loop converted any such exception into a channel Close rather than dropping the packet. One small, unauthenticated packet therefore ends the media session.

This is reachable during ICE connectivity checks — before the DTLS handshake and before any STUN MESSAGE-INTEGRITY verification. Because the RTP/ICE port is shared/advertised in the ICE candidates, a peer or on-path attacker can reach it (exposure is lower for a blind off-path attacker that must first learn the ephemeral port). Impact is availability only — no loss of confidentiality or integrity.

Affected versions

NuGet package SIPSorcery <= 10.0.8.

Patches

Fixed in 10.0.9.

Root cause

Two issues combine:

1. Unchecked indexing of untrusted bytes. - RTPChannel.OnRTPPacketReceived read packet[1] after only checking the packet was non-empty, so a 1-byte packet threw IndexOutOfRangeException. - STUNAttribute.ParseMessageAttributes passed a null/short value to the typed attribute parsers, and STUNXORAddressAttribute (and the non-XOR STUNAddressAttribute) then read attributeValue[1], AsSpan(2) and AsSpan(4) with no length check. A STUN message carrying an XOR-MAPPED-ADDRESS, XOR-PEER-ADDRESS or XOR-RELAYED-ADDRESS attribute of length 0–7 threw (NullReferenceException for length 0, IndexOutOfRangeException/ArgumentOutOfRangeException for 1–7).

1. The UDP receive loop closed the channel on any exception. The catch-all in UdpReceiver.EndReceiveFrom called Close(), tearing down the channel, instead of dropping the offending packet and continuing. This was systemic: any unhandled exception anywhere in the packet pipeline (STUN, RTP, RTCP, DTLS demux, SRTP, TURN) became a channel teardown.

Fix

• UdpReceiver.EndReceiveFrom: a non-socket exception now logs and drops the single packet and re-arms the receive loop (matching the existing SIPUDPChannel behaviour), instead of closing the channel. Genuine socket failures continue to be handled separately.
• RTPChannel.OnRTPPacketReceived: requires a minimum packet length (RTPHeader.MIN_HEADER_LEN) before indexing the discriminator bytes.
• STUN parsing: ParseMessageAttributes validates each attribute value length and skips malformed/truncated attributes; the XOR/address attribute constructors validate length defensively; ParseSTUNMessage no longer dereferences a null attribute list.

Regression tests were added covering the 1-byte packet (channel stays open and remains usable), short/zero-length XOR address attributes (0–7 bytes), and truncated STUN messages.

Workarounds

None within the library short of upgrading. Restricting the RTP/ICE port to known peers at the network layer reduces exposure but does not eliminate it, since a negotiating peer can still trigger the condition.

Credit

Responsibly reported by Lokhesh Ujhoodha.