CVE-2026-91166 in Warpgate
Summary
by MITRE • 09/21/2026
Warpgate is an open source SSH, HTTPS and MySQL bastion host for Linux. From 0.25.0 until 0.27.6, the browser SSH path in warpgate-web-ssh/src/manager.rs handles RCEvent::HostKeyUnknown without the presenting hop identity and instead passes ssh_options.host and ssh_options.port for the final target to KnownHosts::trust. In Prompt and AutoAccept modes, a jump host key can therefore be stored for the target address. A machine later presenting the jump host key at the target address can be accepted as the target, allowing interception of user traffic and a newly issued certificate when certificate authentication is used. The native SSH path is unaffected because it tracks each hop separately. This issue is fixed in version 0.27.6.
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Analysis
by VulDB Data Team • 09/21/2026
Warpgate serves as an open-source bastion host designed to secure access over SSH, HTTPS, and MySQL protocols on Linux systems. Within the specific versions ranging from 0.25.0 through 0.27.6, a critical logic flaw exists in the browser-based SSH implementation located within the warpgate-web-ssh/src/manager.rs module. This vulnerability stems from an incorrect handling of host key verification events during multi-hop connections. Specifically, when the system encounters an RCEvent::HostKeyUnknown condition, it fails to present the identity of the intermediate hop server. Instead, the code erroneously passes the ssh_options.host and ssh_options.port parameters, which correspond to the final target destination, into the KnownHosts::trust function for storage in the known hosts database.
The operational impact of this flaw is significant because it allows an attacker who controls or can spoof a jump host key to manipulate the client's trust store. In Prompt mode, where users are asked to confirm new host keys, and AutoAccept mode, which automatically trusts unknown keys, the user will inadvertently approve storing the jump host's public key under the IP address or hostname of the final target server. This misassociation creates a window for man-in-the-middle attacks on subsequent connections. If an attacker later presents this same jump host key when connecting to what appears to be the original target address, Warpgate will accept it as valid because the stored record matches that destination identity.
This vulnerability effectively bypasses standard SSH host key verification mechanisms intended to prevent impersonation. By accepting a certificate issued by the compromised or spoofed jump host under the guise of the final target, an attacker can intercept user traffic and potentially harvest credentials or sensitive data transmitted through the session. The risk is particularly acute in environments where certificate authentication is utilized for login processes, as the forged identity allows the attacker to obtain newly issued certificates that appear legitimate to downstream systems. It is important to note that this flaw is isolated to the web-based SSH path; the native SSH client implementation remains unaffected because it correctly tracks and verifies each hop separately without conflating identities across different stages of the connection chain.
To mitigate this vulnerability, organizations must ensure they are running Warpgate version 0.27.6 or later, where the logic for handling host key events has been corrected to properly distinguish between intermediate hops and final targets. For environments that cannot immediately upgrade, administrators should exercise extreme caution in AutoAccept mode by manually verifying host keys against out-of-band sources before trusting them. Additionally, implementing strict certificate pinning policies can help detect anomalies even if a jump host key is misassociated with a target address. This issue aligns with CWE-295 Improper Certificate Validation and maps to the MITRE ATT&CK technique T1078 Valid Accounts, as it exploits trust relationships within authentication infrastructure to facilitate unauthorized access or interception.