[Another compression utility with the same race condition issue as bzip2 (CAN-2005-0953) & gzip (CAN-2005-0988) - the file is extracted and file descriptor closed before the file is chmod'ed] ================================ cpio TOCTOU file-permissions vulnerability ================================ Software: cpio Version: cpio 2.6 Software URL: <http://www.gnu.org/software/cpio/> Platform: Unix, Linux. Vulnerability type: Time-of-Check-Time-Of-Use Severity: Low, local user, badly set permissions. Vulnerable software ==================== cpio 2.6 and previous versions running on unix. Vulnerability ============== If a malicious local user has write access to a directory in which a target user is using cpio to extract or compress a file to then a TOCTOU bug can be exploited to change the permission of any file belonging to that user. On decompressing cpio copies the permissions from the compressed cpio file to the uncompressed file. However there is a gap between the uncompressed file being written (and it's file handler being close) and the permissions of the file being changed. During this gap a malicious user can remove the decompressed file and replace it with a hard-link to another file belonging to the user. cpio will then change the permissions on the hard-linked file to be the same as that of the cpio file. The vulnerable line of code can be found on line 581 of the file copyin.c. cpio also use's chmod in a number of other places which may also be vulnerable to exploitation. Workaround ======== Ensure that any directory which is being used by cpio to compress/decompress files is only writeable by the user or alternatively set the sticky bit on the directory's permissions.
