Re: [FD] System Down: A systemd-journald exploit

[Qualys Security Advisory]

Hi all,

Our systemd-journald exploit for CVE-2018-16865 and CVE-2018-16866 is
now available at:

https://www.qualys.com/2019/05/09/system-down/system-down.tar.gz

It is also attached to this email. A few notes about this exploit:

- It supports several targets by default (vulnerable versions of Debian,
  Ubuntu, Fedora, CentOS), and it should be relatively easy to add more
  targets.

- When adding a new amd64 target, use the "free_hook" method if possible
  (if located at a multiple of 16 plus 8, as explained in our advisory);
  for various reasons, the alternative "stderr_chain" method is not as
  reliable as "free_hook" and may therefore take longer to succeed.

- When adding and testing a new target, you may want to set
  "StartLimitInterval=1s" and "StartLimitBurst=10" (for example) in
  "systemd-journald.service": the exploit will detect this and
  brute-force faster.

- If the exploit dies because "No journal files were opened due to
  insufficient permissions", the "wall" method can be used instead (via
  the "-w" switch). Our exploit currently implements the wall method
  "ssh 127.0.0.1", but alternative methods can be implemented
  ("utempter" and "gnome-pty-helper", for example).

- To test the default information-leak method even if "No journal files
  were opened due to insufficient permissions", it is enough to create
  /var/log/journal/ (as explained in "man systemd-journald").

Thank you very much! With best regards,

-- 
the Qualys Security Advisory team


system-down.tar.gz
Description: application/gzip

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[FD] System Down: A systemd-journald exploit

[Qualys Security Advisory]

Qualys Security Advisory

System Down: A systemd-journald exploit



Contents


Summary
CVE-2018-16864
- Analysis
- Exploitation
CVE-2018-16865
- Analysis
- Exploitation
CVE-2018-16866
- Analysis
- Exploitation
Combined Exploitation of CVE-2018-16865 and CVE-2018-16866
- amd64 Exploitation
- i386 Exploitation
Acknowledgments
Timeline

Conversion, software version 7.0
-- System of a Down, "Toxicity"



Summary


We discovered three vulnerabilities in systemd-journald
(https://en.wikipedia.org/wiki/Systemd):

- CVE-2018-16864 and CVE-2018-16865, two memory corruptions
  (attacker-controlled alloca()s);

- CVE-2018-16866, an information leak (an out-of-bounds read).

CVE-2018-16864 was introduced in April 2013 (systemd v203) and became
exploitable in February 2016 (systemd v230). We developed a proof of
concept for CVE-2018-16864 that gains eip control on i386.

CVE-2018-16865 was introduced in December 2011 (systemd v38) and became
exploitable in April 2013 (systemd v201). CVE-2018-16866 was introduced
in June 2015 (systemd v221) and was inadvertently fixed in August 2018.

We developed an exploit for CVE-2018-16865 and CVE-2018-16866 that
obtains a local root shell in 10 minutes on i386 and 70 minutes on
amd64, on average. We will publish our exploit in the near future.

To the best of our knowledge, all systemd-based Linux distributions are
vulnerable, but SUSE Linux Enterprise 15, openSUSE Leap 15.0, and Fedora
28 and 29 are not exploitable because their user space is compiled with
GCC's -fstack-clash-protection.

This confirms https://grsecurity.net/an_ancient_kernel_hole_is_not_closed.php:
"It should be clear that kernel-only attempts to solve [the Stack Clash]
will necessarily always be incomplete, as the real issue lies in the
lack of stack probing."



CVE-2018-16864



Analysis


The waves all keep on crashing by
-- System of a Down, "Suggestions"

We accidentally discovered CVE-2018-16864 while working on the exploit
for Mutagen Astronomy (CVE-2018-14634); if we pass several megabytes of
command-line arguments to a program that calls syslog(), then journald
crashes:

systemd-journal[472]: segfault at 7ffe9a077420 ip 7f45f6174877 sp 
7ffe9a0773f0 error 6 in systemd-journald[7f45f6169000+3f000]

(gdb) disassemble 0x7f45f6174877 - 0x7f45f6169000
Dump of assembler code for function dispatch_message_real.4064:
   ...
   0xb82c <+988>:   callq  0x2bd10 

   0xb831 <+993>:   test   %eax,%eax
   0xb833 <+995>:   js 0xb8ea 
   0xb839 <+1001>:  mov-0x218(%rbp),%rbx
   0xb840 <+1008>:  test   %rbx,%rbx
   0xb843 <+1011>:  je 0xd31b 
   0xb849 <+1017>:  mov%rbx,%rdi
   0xb84c <+1020>:  callq  0x5360 
   0xb851 <+1025>:  add$0xa,%eax
   0xb854 <+1028>:  cltq
   0xb856 <+1030>:  add$0x1e,%rax
   0xb85a <+1034>:  and$0xfff0,%rax
   0xb85e <+1038>:  sub%rax,%rsp
   0xb861 <+1041>:  movabs $0x454e494c444d435f,%rax
   0xb86b <+1051>:  lea0x37(%rsp),%r15
   0xb870 <+1056>:  and$0xfff0,%r15
   0xb874 <+1060>:  test   %rbx,%rbx
   0xb877 <+1063>:  mov%rax,(%r15)
   0xb87a <+1066>:  mov$0x3d,%eax
   0xb87f <+1071>:  mov%ax,0x8(%r15)
   0xb884 <+1076>:  lea0x9(%r15),%rax
   0xb888 <+1080>:  je 0xb895 
   0xb88a <+1082>:  mov%rbx,%rsi
   0xb88d <+1085>:  mov%rax,%rdi
   0xb890 <+1088>:  callq  0x5370 

538 static void dispatch_message_real(
...
604 r = get_process_cmdline(ucred->pid, 0, false, );
605 if (r >= 0) {
606 x = strjoina("_CMDLINE=", t);

919 #define strjoina(a, ...)\
920 ({  \
921 const char *_appendees_[] = { a, __VA_ARGS__ }; \
922 char *_d_, *_p_;\
923 int _len_ = 0;  \
924 unsigned _i_;   \
925 for (_i_ = 0; _i_ < ELEMENTSOF(_appendees_) &&