GHSA-fj7v-r99m-22gq: Pillow TGA RLE encoder can serialize up to ~57 KB of adjacent heap data into generated images

Summary Pillow's TGA RLE encoder reads past its row buffer when saving a mode "1" image. Adjacent process heap bytes can be copied into the generated TGA file. The bug is reachable through the public save API: im.save(out, format="TGA", compression="tga_rle") Older affected Pillow versions use the equivalent public option rle=True. For mode "1", Pillow allocates a packed row buffer of ceil(width / 8) bytes, but ImagingTgaRleEncode() treats the row as one full byte per pixel. The maximum valid TGA width is 65535. At that width: allocated packed row buffer: 8192 bytes encoder byte-offset walk: 65535 bytes maximum OOB window per row: 57343 bytes On non-ASAN Pillow 12.2.0, the public-only maximum-width PoC below serialized 57297 bytes from distinct out-of-bounds source offsets into one returned TGA, covering 99.92% of the maximum adjacent heap window. No heap grooming, ctypes, private API, or malformed input file was used. The disclosure is emitted across many TGA packet payload copies of at most 128 bytes each, not one large memcpy(). Details src/PIL/TgaImagePlugin.py allows mode "1" TGA output and selects the tga_rle encoder when RLE compression is requested. src/encode.c:_setimage() allocates the row buffer using the packed-bit formula: state->bytes = (state->bits * state->xsize + 7) / 8; state->buffer = (UINT8 *)calloc(1, state->bytes); For mode "1", state->bits == 1. src/libImaging/TgaRleEncode.c then computes: bytesPerPixel = (state->bits + 7) / 8; This becomes 1, and the encoder uses pixel indexes as byte offsets: static int comparePixels(const UINT8 *buf, int x, int bytesPerPixel) { buf += x * bytesPerPixel; return memcmp(buf, buf + bytesPerPixel, bytesPerPixel) == 0; } The packet payload memcpy() later copies those out-of-bounds source bytes into the output. Raw packets copy up to 128 contiguous bytes, while RLE packets copy one representative byte: memcpy( dst, state->buffer + (state->x * bytesPerPixel - state->count), flushCount ); A width