CVE-2026-88924 in Red Hat
Summary
by MITRE • 09/10/2026
A flaw was found in the admin backend of gvfs. The privileged gvfsd-admin daemon changes the ownership of newly created private D-Bus sockets by calling the link-following chown() function on a pathname inside a user-controlled directory. A local attacker can exploit this via a Time-of-Check Time-of-Use (TOCTOU) race condition and exchange the socket pathname with a symbolic link pointing to an arbitrary root-owned file (such as /etc/pam.d/su). The daemon subsequently follows the symlink and changes the ownership of the targeted root-owned file to the attacker's user ID. This allows an authenticated local attacker to modify critical system files, leading to a full local privilege escalation to root.
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Analysis
by VulDB Data Team • 09/10/2026
The vulnerability identified in the gvfs admin backend represents a classic but severe implementation error involving improper handling of symbolic links during privileged operations. The core technical flaw resides within the gvfsd-admin daemon, which operates with elevated privileges to manage file system tasks on behalf of users. Specifically, when creating private D-Bus sockets for administrative functions, the daemon utilizes a link-following chown() function call on pathnames located within directories controlled by unprivileged users. This design choice creates a critical security gap because it assumes that the pathname provided will always refer to a regular file or directory created directly by the user, rather than allowing an attacker to manipulate the filesystem structure through symbolic links. By relying on link-following behavior without adequate validation of the final target's attributes prior to the ownership change operation, the daemon fails to enforce strict security boundaries regarding which files can be modified with root privileges.
This architectural weakness enables a Time-of-Check Time-of-Use race condition that allows for local privilege escalation. An authenticated local attacker can exploit this by creating a symbolic link within their controlled directory before or during the moment the privileged daemon attempts to change ownership of the socket pathname. The attacker constructs this symlink to point toward arbitrary root-owned files, such as critical system configuration files like /etc/pam.d/su. When the gvfsd-admin daemon executes its chown() call, it follows the symbolic link rather than treating the path as a simple file creation operation within the user's directory. Consequently, the ownership of the targeted root-owned file is transferred to the attacker's user ID. This transfer of ownership effectively grants the attacker full control over these sensitive system files, bypassing standard permission restrictions that would otherwise prevent modification by non-root users.
The operational impact of this vulnerability is significant, as it facilitates a direct path from an authenticated local account to complete root access on the affected system. Once the attacker has changed the ownership of critical configuration files such as those in /etc/pam.d/, they can modify authentication mechanisms or execute arbitrary commands with elevated privileges. This undermines the fundamental security model of multi-user Linux systems, where privilege escalation should require explicit and secure authorization processes rather than being achievable through race conditions in administrative helper daemons. The ability to alter PAM configuration files specifically allows for persistent access and further exploitation vectors that do not rely on continued existence of this specific gvfs flaw.
From a classification perspective, this vulnerability aligns with CWE-367, which describes Time-of-check Time-of-use (TOCTOU) race conditions in software security. The failure to atomically verify the target file's properties before performing the ownership change is the root cause. Additionally, it relates to CWE-250 regarding execution with unnecessary privileges, as the daemon performs a high-risk operation that could be mitigated by using safer APIs or restricting operations to non-symlink targets. In terms of attack tactics, this exploitation technique maps to MITRE ATT&CK techniques related to privilege escalation and defense evasion through manipulation of system configuration files.
Mitigation strategies should focus on eliminating the race condition at the code level. The most effective remediation involves replacing the link-following chown() call with a mechanism that does not follow symbolic links, such as using O_NOFOLLOW flags when opening file descriptors or utilizing fchown() after opening the file descriptor directly within the user's directory without following symlinks. Alternatively, restricting the gvfsd-admin daemon to operate only on explicitly whitelisted paths outside of user-writable directories would prevent this class of attack entirely. System administrators should also ensure that relevant patches are applied promptly and monitor for unusual changes in ownership of critical system configuration files as an indicator of potential exploitation attempts.