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A flaw was found in qemu Media Transfer Protocol (MTP). The code opening files in usb_mtp_get_object and usb_mtp_get_partial_object and directories in usb_mtp_object_readdir doesn't consider that the underlying filesystem may have changed since the time lstat(2) was called in usb_mtp_object_alloc, a classical TOCTTOU problem. An attacker with write access to the host filesystem shared with a guest can use this property to navigate the host filesystem in the context of the QEMU process and read any file the QEMU process has access to. Access to the filesystem may be local or via a network share protocol such as CIFS.
A flaw was found in qemu Media Transfer Protocol (MTP). The code opening files in usb_mtp_get_object and usb_mtp_get_partial_object and directories in usb_mtp_object_readdir doesn't consider that the underlying filesystem may have changed since the time lstat(2) was called in usb_mtp_object_alloc, a classical TOCTTOU problem. An attacker with write access to the host filesystem shared with a guest can use this property to navigate the host filesystem in the context of the QEMU process and read any file the QEMU process has access to. Access to the filesystem may be local or via a network share protocol such as CIFS.
CVSS 3.0 Base Score 5.3. CVSS Attack Vector: network. CVSS Attack Complexity: high. CVSS Vector: (CVSS:3.0/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N).
CVSS 2.0 Base Score 3.5. CVSS Attack Vector: network. CVSS Attack Complexity: medium. CVSS Vector: (AV:N/AC:M/Au:S/C:P/I:N/A:N).
CVSS 3.1 Base Score 5.3. CVSS Attack Vector: network. CVSS Attack Complexity: high. CVSS Vector: (CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N).
The following code checks a file, then updates its contents.
}updateThings();Potentially the file could have been updated between the time of the check and the lstat, especially since the printf has latency.
The following code is from a program installed setuid root. The program performs certain file operations on behalf of non-privileged users, and uses access checks to ensure that it does not use its root privileges to perform operations that should otherwise be unavailable the current user. The program uses the access() system call to check if the person running the program has permission to access the specified file before it opens the file and performs the necessary operations.
}...
fprintf(stderr,"Unable to open file %s.\n",file);The call to access() behaves as expected, and returns 0 if the user running the program has the necessary permissions to write to the file, and -1 otherwise. However, because both access() and fopen() operate on filenames rather than on file handles, there is no guarantee that the file variable still refers to the same file on disk when it is passed to fopen() that it did when it was passed to access(). If an attacker replaces file after the call to access() with a symbolic link to a different file, the program will use its root privileges to operate on the file even if it is a file that the attacker would otherwise be unable to modify. By tricking the program into performing an operation that would otherwise be impermissible, the attacker has gained elevated privileges. This type of vulnerability is not limited to programs with root privileges. If the application is capable of performing any operation that the attacker would not otherwise be allowed perform, then it is a possible target.
This code prints the contents of a file if a user has permission.
}
}//resolve file if its a symbolic link$filename = readlink($filename);return;return false;This code attempts to resolve symbolic links before checking the file and printing its contents. However, an attacker may be able to change the file from a real file to a symbolic link between the calls to is_link() and file_get_contents(), allowing the reading of arbitrary files. Note that this code fails to log the attempted access (CWE-778).
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