...
A security flaw exists in the code shown below resulting from the absence of proper canonicalization measures on the file path. This allows an attacker to traverse the file system and possibly write to a file of his choice, with the privileges of the vulnerable program. For example, it may be possible to overwrite the password file (such as the /etc/passwd, common to many POSIX based systems) or a device file such as the mouse which in turn can aid further exploitation or cause a denial of service to occur.
| Code Block | ||
|---|---|---|
| ||
enum {array_mex = 100}; /* * Program running with elevated privileges where argv[1] * and argv[2] are supplied by the user */ char x[100array_max]; FILE *fp = fopen(argv[1], "w"); strncpy(x, argv[2], 100array_max); x[100array_max - 1] = '\0'; /* * Write operation to an unintended file like /etc/passwd * gets executed */ fwrite(x, sizeof(x[0]), sizeof(x)/sizeof(x[0]), fp); |
...
| Code Block | ||
|---|---|---|
| ||
/*
* Make sure that the chroot/jail directory exists within
* the current working directory. Also assign appropriate
* permissions to the directory to restrict access. Close
* all file system descriptors to outside resources lest
* they escape the jail.
*/
if (setuid(0) == -1) {
/* Handle Error */
}
if (chroot("chroot/jail") == -1) {
/* Handle Error */
}
if (chdir("/") == -1) {
/* Handle Error */
}
/* Drop privileges permanently */
if (setgid(getgid()) == -1) {
/* Handle Error */
}
if (setuid(getuid()) == -1) {
/* Handle Error */
}
/* Perform unprivileged operations */
enum {array_mex = 100};
FILE *fp = fopen(argv[1], "w");
char x[100array_max];
strncpy(x, argv[2], 100array_max);
x[100array_max - 1] = '\0';
/* Write operation safe is safe within jail */
fwrite(x, sizeof(x[0]), sizeof(x)/sizeof(x[0]), fp);
|
...