fix: skip message body for unknown types in AgentProtocol#1493
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rado0x54 wants to merge 1 commit intomscdex:masterfrom
Open
fix: skip message body for unknown types in AgentProtocol#1493rado0x54 wants to merge 1 commit intomscdex:masterfrom
rado0x54 wants to merge 1 commit intomscdex:masterfrom
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The default case in the AgentProtocol message parser did not advance the read position past the message body for unrecognized message types. In server mode this left body bytes in the parse buffer, corrupting subsequent message parsing. Apply the same defensive skip in client mode where cb(error) aborts the stream but could leave a corrupted buffer if the caller catches and continues. OpenSSH >=8.9 sends SSH_AGENTC_EXTENSION (27) messages such as session-bind@openssh.com for host-key binding before identity requests, which is the real-world trigger for this bug. See PROTOCOL.agent §4.7 in the OpenSSH source.
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Summary
The
defaultcase inAgentProtocol's message parser does not advance the read position past the message body for unrecognized message types. In server mode, this leaves the body bytes in the parse buffer, corrupting all subsequent message parsing. This patch applies the same defensive skip in client mode as well.Real-world trigger: OpenSSH >=8.9 sends
SSH_AGENTC_EXTENSION(type 27) messages — specificallysession-bind@openssh.comfor host-key binding — to the agent before identity requests. Without this fix, the extension body bytes corrupt the followingSSH_AGENTC_REQUEST_IDENTITIESparse, causing agent forwarding to fail silently.See PROTOCOL.agent §4.7 in the OpenSSH source.
Changes
lib/agent.js: Addp += this[SYM_MSGLEN] - 1in thedefaultcase of both the server-mode and client-mode message parsers to skip past unrecognized message bodies.test/test-agent-protocol-extension.js: New test file covering:Test plan
node test/test-agent-protocol-extension.js)session-bind@openssh.comis sent