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Crashmon - A LLDB Based replacement for CrashWrangler

· 3 min read
ant4g0nist
Crashmon - A CrashWrangler replacement based on LLDB. Crashmon, same as CrashWrangler, is a LLDB wrapper together with [Lisa.py](https://github.com/ant4g0nist/lisa.py) that can be used to determine if a crash is an exploitable security issue, and if a crash is a duplicate of another known crash.

Usage

Build Instruction

macOSResearch ✗ git clone https://github.com/ant4g0nist/crashmon
macOSResearch ✗ cd crashmon
crashmon git:(main) ✗ make
crashmon git:(main) ✗ make install

example

For debugging macOS System Applications/Services, it is expected that you disable SIP as crashmon uses LLDB.

Environment Variable Reference

CW_CURRENT_CASE:

Path of the test case file that is being open in the target application. If set, crashmon will read and save the content of the test case file to triaged crash folder. This will be handy while fuzzing!

CW_ATTACH_PID:

If set, use this pid as the process to monitor for crashes.
e.g.

env CW_ATTACH_PID=12313 CW_CURRENT_CASE=foo ./crashmon

or

sudo env CW_ATTACH_PID=12313 CW_CURRENT_CASE=foo ./crashmon

CW_LOG_DIR:

  • The directory to output crashlogs to.
  • Default ./crashlogs

CW_JSON_STDOUT:

  • Write exploitable output as json to stdout.
  • Default false

CWE_*:

If there are any environment variables prefixed with CWE_, delete the prefix and set the environment variable in the child. This does not apply when using CW_ATTACH_PID or CW_REGISTER_LAUNCHD_NAME.

crashmon return values

  • No crash = 0
  • Crash = 1
  • Timeout = 2

Exploitability algorithm

The algorithm for determining exploitability looks like this:

Exploitable if:

  • Crash on write instruction
  • Crash executing invalid address
  • Crash calling an invalid address
  • Illegal instruction exception
  • Abort due to -fstack-protector, _FORTIFY_SOURCE, heap corruption detected
  • Stack trace of crashing thread contains certain functions such as malloc, free, szone_error, objc_MsgSend, etc.

Not exploitable if:

  • Divide by zero exception
  • Stack grows too large due to recursion
  • Null dereference(read or write)
  • Other abort
  • Crash on read instruction

PS

This is meant to be used just as an initial triage system! Don't really 100% on the crashmon's output as there might be bugs in lisa.py. I appreciate pull requests.

So, it's recommended to run the test case again with libgmalloc(3) on, and see if the crash changes to one that is considered to be exploitable.

todo

  • add lisa.py exploitable checks
  • test moreeee
  • follow xpc services (target function -> 'xpc_connection_get_pid'. Usecase: Safari->WebContent)

thanks

  • @apple for crashwrangler
  • LLVM