Description

ImageMagick has a Heap Buffer Overflow in InterpretImageFilename

Heap Buffer Overflow in InterpretImageFilename

Summary

A heap buffer overflow was identified in the InterpretImageFilename function of ImageMagick. The issue stems from an off-by-one error that causes out-of-bounds memory access when processing format strings containing consecutive percent signs (%%).

Environment

OS: Arch Linux (Linux gmkhost 6.14.2-arch1-1 # 1 SMP PREEMPT_DYNAMIC Thu, 10 Apr 2025 18:43:59 +0000 x86_64 GNU/Linux (GNU libc) 2.41)

Architecture: x86_64

Compiler: gcc (GCC) 15.1.1 20250425

Reproduction

Build Instructions

# Clone the repository
git clone https://github.com/ImageMagick/ImageMagick.git
cd ImageMagick
git reset --hard 8fff9b4f44d2e8b5cae2bd6db70930a144d15f12

# Build with AddressSanitizer
export CFLAGS="-fsanitize=address -g -O1"
export CXXFLAGS="-fsanitize=address -g -O1"...
Show more

Minimum Trigger

./utilities/.libs/magick %% [any_output_filename]

Crash Analysis

AddressSanitizer Output

$ ./utilities/.libs/magick %% a
=================================================================
==2227694==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x7037f99e3ad3 at pc 0x741801e81a17 bp 0x7ffd22fa4e00 sp 0x7ffd22fa45b8
READ of size 1 at 0x7037f99e3ad3 thread T0
    #0 0x741801e81a16 in strchr /usr/src/debug/gcc/gcc/libsanitizer/sanitizer_common/sanitizer_common_interceptors.inc:746
    #1 0x7418013b4f06 in InterpretImageFilename MagickCore/image.c:1674
    #2 0x7418012826a3 in ReadImages MagickCore/constitute.c:1040
    #3 0x741800e4696b in CLINoImageOperator MagickWand/operation.c:4959...
Show more

Root Cause Analysis

The first command line argument is interpreted as MagickImageCommand: https://github.com/ImageMagick/ImageMagick/blob/8fff9b4f44d2e8b5cae2bd6db70930a144d15f12/utilities/magick.c#L83

const CommandInfo
  MagickCommands[] =
  {
    MagickCommandSize("magick", MagickFalse, MagickImageCommand),

It is invoked here: https://github.com/ImageMagick/ImageMagick/blob/8fff9b4f44d2e8b5cae2bd6db70930a144d15f12/MagickWand/magick-cli.c#L220

status=command(image_info,argc,argv,&text,exception);

The execution then follows this path:

https://github.com/ImageMagick/ImageMagick/blob/8fff9b4f44d2e8b5cae2bd6db70930a144d15f12/MagickWand/magick-cli.c#L1387

https://github.com/ImageMagick/ImageMagick/blob/8fff9b4f44d2e8b5cae2bd6db70930a144d15f12/MagickWand/magick-cli.c#L586

https://github.com/ImageMagick/ImageMagick/blob/8fff9b4f44d2e8b5cae2bd6db70930a144d15f12/MagickWand/magick-cli.c#L419

https://github.com/ImageMagick/ImageMagick/blob/8fff9b4f44d2e8b5cae2bd6db70930a144d15f12/MagickWand/operation.c#L5391

https://github.com/ImageMagick/ImageMagick/blob/8fff9b4f44d2e8b5cae2bd6db70930a144d15f12/MagickWand/operation.c#L5473

https://github.com/ImageMagick/ImageMagick/blob/8fff9b4f44d2e8b5cae2bd6db70930a144d15f12/MagickWand/operation.c#L4959

https://github.com/ImageMagick/ImageMagick/blob/8fff9b4f44d2e8b5cae2bd6db70930a144d15f12/MagickCore/constitute.c#L1009

https://github.com/ImageMagick/ImageMagick/blob/8fff9b4f44d2e8b5cae2bd6db70930a144d15f12/MagickCore/constitute.c#L1039

https://github.com/ImageMagick/ImageMagick/blob/8fff9b4f44d2e8b5cae2bd6db70930a144d15f12/MagickCore/image.c#L1649

https://github.com/ImageMagick/ImageMagick/blob/8fff9b4f44d2e8b5cae2bd6db70930a144d15f12/MagickCore/image.c#L1674

The execution eventually reaches InterpretImageFilename and enters a loop. The format variable here is "%%". At this point, it is safe to access *(format + 2) but not safe to access *(format + 3).

for (p=strchr(format,'%'); p != (char *) NULL; p=strchr(p+1,'%'))
{
  q=(char *) p+1;
  if (*q == '%')
    {
      p=q+1;
      continue;
    }...
Show more

The first strchr call returns a pointer equal to format and assigns it to p. Then q is initialized with p + 1 (format + 1), and *q is '%', so the code enters the if branch. Here, p is reassigned to q + 1 (format + 2).

In the next iteration, p + 1 (format + 3) is passed to strchr, and when strchr accesses it, this causes an out-of-bounds read.

Mitigation

Aliases

References