CVE-2026-78662 in x-crypto-ssh
Summary
by MITRE • 09/02/2026
Previously, a channel registered in the mux's chanList is not usable until it is established. A malicious peer was able flood the channel's incomingRequests, deadlocking the entire connection. Now, we add an atomic established state, set when a channel becomes usable. Until such a time, handlePacket drops every packet other than the open confirmation/failure, without blocking and without tearing down the connection.
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Analysis
by VulDB Data Team • 09/02/2026
The vulnerability described involves a race condition or logic error in the handling of multiplexed connections, specifically within the management of channels registered in a channel list prior to their full establishment. In many network protocols that utilize multiplexing, such as HTTP/2 or similar stream-based architectures, multiple logical streams are carried over a single physical connection. A critical phase exists between the initiation of a new channel and its final acceptance by both peers. During this window, if the implementation does not properly filter incoming requests destined for an unestablished channel, it creates a significant availability risk. Specifically, a malicious peer can exploit this gap by flooding the incoming request queue associated with that specific channel identifier before the connection is fully negotiated or established. This flood of invalid or premature packets consumes processing resources and memory buffers without being correctly discarded, leading to a deadlock state where the entire multiplexed connection becomes unresponsive.
From a technical perspective, the root cause lies in the lack of atomic state management for channels during their lifecycle transition from pending to active. Previously, once a channel was registered in the mux's internal list, it became immediately eligible to receive and process incoming packets. This design flaw allowed an attacker to send a high volume of data or control frames targeting that specific channel ID while it was still in a transitional state. Because the system attempted to handle these packets rather than dropping them silently or queuing them safely without blocking critical resources, the internal request queue could become saturated. Once this saturation occurs, subsequent legitimate traffic cannot be processed because the thread or goroutine responsible for handling packet logic is blocked waiting on full queues or encountering resource exhaustion conditions. This results in a denial of service that affects not just the targeted channel but potentially the entire connection if shared resources are impacted.
The operational impact of this vulnerability is severe, primarily manifesting as a Denial of Service (DoS). By exploiting the window where channels are registered but not yet established, an attacker can effectively freeze communication for all streams sharing the same multiplexed connection. This disrupts service availability and can lead to cascading failures in systems relying on persistent connections for performance efficiency. The inability to distinguish between valid post-establishment traffic and premature pre-establishment traffic means that any peer with network access can degrade or halt service by simply sending a burst of packets targeting new channel IDs immediately after initiating them. This undermines the reliability guarantees expected from multiplexed protocols, where isolation between streams is crucial for maintaining overall system stability.
To mitigate this vulnerability, the implementation introduces an atomic established state flag that tracks whether a channel has completed its handshake or initialization process. With this change, the packet handling logic is modified to strictly filter incoming data based on this status. Before processing any packet destined for a specific channel, the system now checks if the channel's established flag is set to true. If the channel is not yet established, all packets except for the initial open confirmation or failure messages are dropped immediately and silently. This approach prevents resource exhaustion by ensuring that premature traffic does not consume significant memory or processing cycles in request queues. Furthermore, this filtering occurs without blocking other operations on the connection, thereby preserving the responsiveness of active channels even when an attacker attempts to flood a new one.
This fix aligns with best practices for secure multiplexing and state management as outlined in various industry standards. The issue relates closely to CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization, where shared resources (the channel's request queue) are accessed without proper synchronization of their lifecycle states. Additionally, the attack vector corresponds to ATT&CK technique T1498: Network Denial of Service, specifically involving resource exhaustion through flooding. By enforcing strict state checks before processing traffic, the system ensures that only valid, established channels participate in data exchange, thereby closing the window for exploitation and maintaining the integrity and availability of the multiplexed connection infrastructure.