gvfs vulnerabilities

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.

A flaw was found in the MTP backend in gvfs. When reading a file from a mounted MTP device, do_read() in gvfsbackendmtp.c trusts the data length returned by the device without limiting it to the original size requested by the client. If a malicious MTP device responds with more bytes than requested, this unrestricted length is passed directly to memcpy(). This causes the operation to read memory outside the intended boundaries. This allows an attacker who plugs in a malicious MTP device to cause a segmentation fault when a file is read and crash the gvfsd-mtp process, resulting in a denial of service.

A flaw was found in the AFP backend in gvfs. When mounting a share, a malicious AFP server can cause the DSI read path to process a length that exceeds the size requested by the client. The function does not verify the server-provided length against the pre-sized reply buffer, causing the operation to access past the intended boundaries. This issue allows a malicious server to overflow a heap buffer and crash the gvfsd-afp process, resulting in a denial of service.

A flaw was found in the SFTP backend in gvfs. When mounting a share and reading a file, a malicious SFTP server can cause read_reply() to process a length that exceeds the size requested by the client, leading to out-of-bounds write. This can corrupt heap memory in the gvfsd-sftp process, resulting in denial of service or potentially arbitrary code execution.

A flaw was found in the SFTP backend in gvfs. When mounting a share, a malicious SFTP server can cause read_string() to allocate a buffer with a certain length but the function does not verify that the buffer is completely filled, leaving the remainder of the buffer containing uninitialized heap contents. If the server sends a short FXP_HANDLE reply, these uninitialized bytes are taken as the file handle. The client will then echo these uninitialized bytes back to the server on all subsequent requests using that handle. With a length of 128 bytes, this issue allows the malicious server to deterministically read uninitialized heap memory from the gvfsd-sftp process, leaking its heap base and the load address of the libgio library, resulting in a deterministic defeat of Address Space Layout Randomization (ASLR).