±--------------------------------------------------------+
| XADV-2013002 glibc 2.5 <= reloc types to crash bug |
±--------------------------------------------------------+

Vulnerable versions:

• glibc 2.5 <=
  Not vulnerable versions:
• glibc 2.6 >=
  Testbed: linux distro
  Type: Local
  Impact: crash
  Vendor: https://www.gnu.org/software/libc
  Author: x90c <geinblues nospam gmail dot com>
  Site: x90c.org

=========
ABSTRACT:

[Unspecified reloc types bug]
'defaults:' label codes on If not defined RTLD_BOOTSTRAP, glibc 2.5
defined RTLD_BOOTSTRAP default. The elf_machine_rel() of the
vulnerable glibc 2.5 ld-2.5.so doesn't process 'defaults:' In
the symbol relocation time. It means the ELF object 4bytes
altered with unspecified reloc types to crash.
('defaults:' label process unspecified reloc types to
calc reloc addr)

The vulnerable function sets *reloc_addr_arg as 5rd argument
(to reloc addr). and calc reloc addr. The unspecified reloc types
passed Improper value(on elf binary) on reloc_addr. An elf binary
with altered unspecified reloc_types to crash. BUG!

The bug can be used for rootkit technique via altering the ELF object.

=========
DETAILS:

glibc-2.5/dl-machine.h

auto inline void
__attribute ((always_inline))
elf_machine_rel (struct link_map *map, const Elf32_Rel *reloc,
const Elf32_Sym *sym, const struct r_found_version *version,
void *const reloc_addr_arg)
{
// reloc_addr = reloc_addr_arg(5rd argument as relative jump)
Elf32_Addr *const reloc_addr = reloc_addr_arg;

…

  switch (r_type)	
{

case R_386_GLOB_DAT:
case R_386_JMP_SLOT:
      // *reloc_addr(*relocation addr) = value(relative addr calculated at above codes.)
  *reloc_addr = value;
  break;
}
// XXX BUG: 'defaults:' label not exists!

…

}
#endif /* !RTLD_BOOTSTRAP */

===============
EXPLOIT CODES:

Altering reloc types on the ELF binary.

=============
PATCH CODES:

add 'defaults:' label on above relocation code
If RTLD_BOOTSTRAP defined.

===============
VENDOR STATUS:

2012/09/04 - The bug Discovered.
2013/10/20 - Advisory released on full-disclosure, bugtraq, exploit-db.

==============
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============
DISCLAIMER:

The authors reserve the right not to be responsible for the topicality,
correctness, completeness or quality of the information provided in this
document. Liability claims regarding damage caused by the use of any information
provided, including any kind of information which is incomplete or incorrect,
will therefore be rejected.