CVE-2026-68930 in russh
Summary
by MITRE • 08/03/2026
Russh is a Rust SSH client & server library. Prior to 0.62.5, russh dispatches channel-scoped Handler callbacks for recipient channel IDs that were never opened or confirmed in russh/src/server/encrypted.rs, server_read_authenticated, and the exec_request callback. Version 0.62.5 fixes the issue.
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Analysis
by VulDB Data Team • 08/03/2026
The vulnerability in Russh library affects versions prior to 0625 where the SSH server implementation contains a critical flaw in channel management that could lead to improper callback execution. This issue resides within the server encrypted module at specific locations including server_read_authenticated function and exec_request callback handling. The core problem occurs when the system dispatches channel-scoped handler callbacks to recipient channel IDs that were never properly opened or confirmed during the SSH session establishment process. This represents a classic case of improper input validation and resource management where the library fails to verify that channel identifiers correspond to actual established communication pathways before executing associated callback functions.
The technical flaw stems from inadequate channel state verification within the server-side implementation, allowing malicious actors to potentially exploit this behavior by crafting specific SSH protocol sequences that trigger callbacks against non-existent or unconfirmed channels. This vulnerability creates a potential attack surface where unauthorized code execution or information disclosure could occur through improper callback invocation. The flaw directly relates to CWE-835 which addresses infinite loops and related vulnerabilities in programming constructs, though more specifically it manifests as an improper handling of channel state transitions within the SSH protocol implementation.
From an operational impact perspective, this vulnerability compromises the integrity of the SSH server implementation by potentially allowing execution of unauthorized callback handlers against channels that should never have been accessible to the callback mechanism. Attackers could exploit this to execute arbitrary code or cause denial of service conditions depending on how the callbacks are implemented within applications using the Russh library. The issue affects any application using Russh versions prior to 0625 that implements server-side SSH functionality with channel management, creating a security risk that could be leveraged for privilege escalation or information theft.
The fix implemented in version 0.62.5 addresses this by properly validating channel states before dispatching callbacks, ensuring that only channels that have been successfully opened and confirmed are processed through the callback mechanism. This remediation follows established security practices by implementing proper input validation and state checking mechanisms as recommended in the ATT&CK framework for server-side exploitation techniques. The solution demonstrates proper secure coding principles by preventing unauthorized access to system resources through improved channel lifecycle management and callback execution controls. Organizations using Russh should immediately upgrade to version 0625 or later to mitigate this vulnerability, particularly those implementing SSH server functionality with complex channel handling requirements where such security flaws could have significant operational consequences.