CVE-2021-46822 (C, published 2022-06-18T16:15Z)
Description: value: The PPM reader in libjpeg-turbo through 2.0.90 mishandles use of tjLoadImage for loading a 16-bit binary PPM file into a grayscale buffer and loading a 16-bit binary PGM file into an RGB buffer. This is related to a heap-based buffer overflow in the get_word_rgb_row function in rdppm.c.
Severity: MEDIUM (CVSS v3 base score: 5.5)
Weakness: CWE-787 \u2014 Out-of-bounds Write
The product writes data past the end, or before the beginning, of the intended buffer.
Repository: https://github.com/libjpeg-turbo/libjpeg-turbo
Files changed:
ChangeLog.md
rdppm.c
Commit message: tjLoadImage: Fix issues w/loading 16-bit PPMs/PGMs

- The PPM reader now throws an error rather than segfaulting (due to a
  buffer overrun) if an application attempts to load a 16-bit PPM file
  into a grayscale uncompressed image buffer.  No known applications
  allowed that (not even the test applications in libjpeg-turbo),
  because that mode of operation was never expected to work and did not
  work under any circumstances.  (In fact, it was necessary to modify
  TJBench in order to reproduce the issue outside of a fuzzing
  environment.)  This was purely a matter of making the library bow out
  gracefully rather than crash if an application tries to do something
  really stupid.

- The PPM reader now throws an error rather than generating incorrect
  pixels if an application attempts to load a 16-bit PGM file into an
  RGB uncompressed image buffer.

- The PPM reader now correctly loads 16-bit PPM files into extended
  RGB uncompressed image buffers.  (Previously it generated incorrect
  pixels unless the input colorspace was JCS_RGB or JCS_EXT_RGB.)

The only way that users could have potentially encountered these issues
was through the tjLoadImage() function.  cjpeg and TJBench were
unaffected.


Vulnerable code:
 * Copyright (C) 2015-2017, 2020, D. R. Commander.
    *ptr++ = rescale[temp];
    *ptr++ = rescale[temp];
    *ptr++ = rescale[temp];
      source->pub.get_pixel_rows = get_word_gray_row;
      source->pub.get_pixel_rows = get_word_rgb_row;

Fixed code:
7. The PPM reader now throws an error, rather than segfaulting (due to a buffer
overrun) or generating incorrect pixels, if an application attempts to use the
`tjLoadImage()` function to load a 16-bit binary PPM file (a binary PPM file
with a maximum value greater than 255) into a grayscale image buffer or to load
a 16-bit binary PGM file into an RGB image buffer.

8. Fixed an issue in the PPM reader that caused incorrect pixels to be
generated when using the `tjLoadImage()` function to load a 16-bit binary PPM
file into an extended RGB image buffer.

 * Copyright (C) 2015-2017, 2020-2021, D. R. Commander.
  register int rindex = rgb_red[cinfo->in_color_space];
  register int gindex = rgb_green[cinfo->in_color_space];
  register int bindex = rgb_blue[cinfo->in_color_space];
  register int aindex = alpha_index[cinfo->in_color_space];
  register int ps = rgb_pixelsize[cinfo->in_color_space];
    ptr[rindex] = rescale[temp];
    ptr[gindex] = rescale[temp];
    ptr[bindex] = rescale[temp];
    if (aindex >= 0)
      ptr[aindex] = 0xFF;
    ptr += ps;
      if (cinfo->in_color_space == JCS_GRAYSCALE)
        source->pub.get_pixel_rows = get_word_gray_row;
      else
        ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
      if (IsExtRGB(cinfo->in_color_space))
        source->pub.get_pixel_rows = get_word_rgb_row;
      else
        ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);