CVE-2026-110923 in Red Hat
Summary
by MITRE • 10/15/2026
A flaw was found in OpenSSH. During an sftp copy, a malicious server can supply an empty name, a slash-only path, or a ".." basename that sftp uses as the local destination, writing outside the directory the user selected.
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Analysis
by VulDB Data Team • 10/15/2026
The vulnerability identified in OpenSSH represents a critical security flaw within the Secure File Transfer Protocol (SFTP) client implementation, specifically affecting how file names and paths are processed during copy operations. This issue arises from insufficient validation of path components received from an untrusted or malicious SFTP server. When a user initiates a download operation using commands such as get or mget, the client relies on metadata provided by the remote server to determine the local filename for saving the transferred data. In this flawed scenario, the server can manipulate these metadata fields by supplying empty strings, paths consisting solely of slashes, or directory traversal sequences like double dots in the basename field. The OpenSSH SFTP client fails to sanitize or validate these inputs before using them as destination file names on the local filesystem.
This lack of input validation leads directly to a path traversal vulnerability that allows an attacker to write files outside the intended working directory. By exploiting this behavior, a malicious server can force the client to save downloaded content into arbitrary locations on the victim's system. For instance, if the user is operating in their home directory and requests a file with an empty name or a parent directory reference, the resulting local path may resolve to sensitive areas such as /etc/passwd, root-owned directories, or other critical configuration files depending on the privileges of the running process. This effectively bypasses the sandboxing expectations users have when using secure transfer tools, turning a trusted utility into a vector for arbitrary file write attacks.
The operational impact of this vulnerability is severe, particularly in environments where automated scripts or unattended processes interact with external SFTP servers. An attacker controlling a malicious server can overwrite critical system files, inject malicious code into executable directories, or corrupt configuration data by exploiting the trust relationship inherent in SSH connections. If the OpenSSH client is running with elevated privileges, such as during root-level automation tasks, the consequences escalate to full remote code execution and complete compromise of the host system. Even for standard users, the ability to write files outside the home directory can lead to privilege escalation if combined with other local vulnerabilities or misconfigurations that allow execution of newly written files from world-writable directories like /tmp.
From a classification perspective, this flaw aligns closely with CWE-22: Improper Limitation of a Pathname to a Restricted Directory and CWE-73: External Control of File Name or Path. These categories highlight the failure to enforce strict boundaries on file system operations based on external input. In terms of adversary tactics, this vulnerability supports techniques found in the MITRE ATT&CK framework under T1083: File and Directory Discovery and potentially T1564: Hidden Files and Directories if used obliquely, though its primary utility lies in initial access or persistence through arbitrary file writes (T1105). The attack vector is remote via network communication but requires the user to actively initiate a transfer from a compromised server.
Mitigation strategies must focus on both immediate patching and long-term defensive coding practices. Organizations should immediately apply vendor-provided patches that update OpenSSH to versions where this path validation logic has been corrected. Developers reviewing similar codebases should implement strict canonicalization of file paths before any filesystem operations occur, ensuring that the resolved absolute path remains within an allowed base directory using techniques such as realpath or equivalent secure library functions. Additionally, input sanitization routines must explicitly reject empty strings and traversal sequences in filename fields received from external sources. Security teams should also audit automation scripts to ensure they do not rely on default behaviors of SFTP clients without explicit destination specifications, thereby reducing the attack surface for similar path manipulation exploits in future iterations or related tools.