OpenSSH File Transfer and Auth Security Flaws

Memory corruption in the OpenSSH client (ssh) before 10.4 lets a malicious or compromised SSH server trigger a use-after-free on the connecting client by changing its host key during a key re-exchange (rekey), potentially leading to information disclosure or code execution in the client process. Only the client side is affected; the server is not vulnerable. There is no public exploit identified at time of analysis and it is not on CISA KEV, and EPSS is low (0.25%, 16th percentile), but the flaw is fixed in OpenSSH 10.4/10.4p1.

Security-control bypass in OpenSSH sshd before 10.4 causes the DisableForwarding=yes hardening directive to be silently ignored when PermitTunnel=yes is also set, so tun-device forwarding remains available despite an administrator's explicit policy to disable all forwarding. Affected operators are those who rely on DisableForwarding as a defense-in-depth restriction; the flaw lets an authenticated user establish layer-2/3 tunnels the configuration was meant to forbid. There is no public exploit identified at time of analysis, EPSS is low (0.13%, 3rd percentile), and it is not on CISA KEV.

Denial of service in OpenSSH sshd before 10.4 lets remote unauthenticated attackers exhaust server resources by driving excessive authentication attempts, because the MaxAuthTries cap was not correctly enforced for the GSSAPIAuthentication path. Only deployments that have enabled GSSAPI-based authentication are exposed, and there is no public exploit identified at time of analysis. EPSS is low (0.34%, 26th percentile) and CISA SSVC records no observed exploitation, so this is a real but non-urgent availability issue rather than a code-execution threat.

OpenSSH sshd before version 10.4 silently ignores the GSSAPIStrictAcceptorCheck configuration directive when the server is integrated with Windows Active Directory, defeating a security control that administrators rely on to enforce GSSAPI acceptor name validation during Kerberos-based SSH authentication. This undocumented behavior means AD-joined SSH servers may accept GSSAPI authentications against unintended Kerberos service principals regardless of how the option is configured, yielding limited confidentiality and integrity impact. No public exploits or active exploitation have been identified; the CVSS AC:H rating reflects the specific environmental prerequisites required for exploitation.

OpenSSH sshd before version 10.4 fails to consistently enforce its built-in minimum authentication delay, undermining the rate-limiting defense designed to slow credential-guessing attacks against SSH services. All OpenSSH releases prior to 10.4 are affected across all platforms, enabling unauthenticated remote attackers to submit authentication attempts at a rate higher than the daemon intends to permit. No public exploit code has been identified and the vulnerability is absent from CISA KEV; however, the trivial attack complexity combined with OpenSSH's near-universal deployment footprint makes prompt patching appropriate.

Path traversal in the OpenSSH sftp client before version 10.4p1 allows an attacker-controlled server to write downloaded files outside the user's intended target directory when the 'sftp server:/path .' bulk-download syntax is used. Affected are all OpenSSH deployments where users sftp from untrusted or attacker-controlled hosts, which in practice spans virtually every Linux and Unix environment. No public exploit has been identified at time of analysis and the vulnerability is not listed in CISA KEV, though the ubiquity of OpenSSH elevates aggregate exposure despite the moderate per-instance severity.

Path traversal in the scp utility of OpenSSH before 10.4 causes files to be written into the parent directory of the intended destination during remote-to-remote copy operations. The root cause is CWE-23 (Relative Path Traversal): scp fails to canonicalize or sanitize paths when relaying data between two remote hosts, allowing an attacker controlling a malicious endpoint to influence where transferred files land. No public exploit identified at time of analysis, and active exploitation has not been confirmed by CISA KEV; the CVSS AC:H and UI:R metrics significantly constrain real-world exploitability.

OpenSSH's internal-sftp subsystem silently discards all command-line arguments beyond position 9, allowing authenticated SFTP users to bypass security restrictions that administrators intended to enforce via those later-positioned arguments. All OpenSSH releases before 10.4 are affected when sshd_config supplies more than nine arguments to the internal-sftp subsystem, which is a non-default but legitimate administrative pattern used for directory restriction, read-only enforcement, and umask control. No public exploit has been identified and this vulnerability is not listed in the CISA KEV catalog; however, sites relying on complex internal-sftp argument chains for access policy enforcement face a direct, silent policy bypass.