GHSA-VJC4-5QP5-M44J

Vulnerability from github – Published: 2026-07-20 23:18 – Updated: 2026-07-20 23:18
VLAI
Summary
Pillow JPEG2000 tiled decode retains a growing scratch buffer and can be used for denial of service
Details

Summary

src/libImaging/Jpeg2KDecode.c:853 accumulates total_component_width across every tile in a JPEG2000 image instead of recomputing it per tile. That accumulated value is then used in the tile_bytes calculation at src/libImaging/Jpeg2KDecode.c:868, which can make the decoder grow state->buffer via realloc at src/libImaging/Jpeg2KDecode.c:876 up to roughly one full image's decompressed size even when each tile is small. A crafted tiled JPEG2000 file can therefore force substantially higher transient memory usage and trigger out-of-memory failures during decoding. Based on current evidence, the supported impact is denial of service, not memory corruption.

Details

  • Location: src/libImaging/Jpeg2KDecode.c:853
  • Root cause: total_component_width is initialized only once before the tile loop and keeps growing across tiles. It is then used to derive tile_bytes, so later tiles are treated as if they had the combined component width of all earlier tiles.
  • Dangerous operation: tile_bytes is promoted into tile_info.data_size, then state->buffer is grown with realloc at src/libImaging/Jpeg2KDecode.c:876.
  • Reachability: any attacker-controlled JPEG2000 image with many tiles reaches this path during normal Image.open(...).load() decoding.

PoC

The attached helper script and testcase were used: exercise_j2k_tile_realloc.zip

Generate the testcase:

pythonexercise_j2k_tile_realloc.py make poc_3664_rgba_tile1832.jp2 \
  --size 3664 --tile 1832

Expected geometry from the helper:

  • image size: 3664 x 3664
  • mode: RGBA
  • tile size: 1832 x 1832 (2x2 tiles)
  • image_bytes=53699584
  • uncapped RSS observed:
  • vulnerable build: maxrss_kb=180264
  • fixed comparison build: maxrss_kb=138404

Load it with the current vulnerable build:

python exercise_j2k_tile_realloc.py load poc_3664_rgba_tile1832.jp2

Load it again under a 160 MB address-space cap:

python exercise_j2k_tile_realloc.py load poc_3664_rgba_tile1832.jp2 --limit-mb 160

Impact

Conservative impact: denial of service through memory exhaustion during JPEG2000 decoding.

Severity
8.7 (High)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
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{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "pillow"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "8.2.0"
            },
            {
              "fixed": "12.3.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-59204"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-770",
      "CWE-789"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-20T23:18:32Z",
    "nvd_published_at": "2026-07-14T16:17:02Z",
    "severity": "HIGH"
  },
  "details": "### Summary\n`src/libImaging/Jpeg2KDecode.c:853` accumulates `total_component_width` across every tile in a JPEG2000 image instead of recomputing it per tile. That accumulated value is then used in the `tile_bytes` calculation at `src/libImaging/Jpeg2KDecode.c:868`, which can make the decoder grow `state-\u003ebuffer` via `realloc` at `src/libImaging/Jpeg2KDecode.c:876` up to roughly one full image\u0027s decompressed size even when each tile is small. A crafted tiled JPEG2000 file can therefore force substantially higher transient memory usage and trigger out-of-memory failures during decoding. Based on current evidence, the supported impact is denial of service, not memory corruption.\n\n### Details\n- Location: `src/libImaging/Jpeg2KDecode.c:853`\n- Root cause: `total_component_width` is initialized only once before the tile loop and keeps growing across tiles. It is then used to derive `tile_bytes`, so later tiles are treated as if they had the combined component width of all earlier tiles.\n- Dangerous operation: `tile_bytes` is promoted into `tile_info.data_size`, then `state-\u003ebuffer` is grown with `realloc` at `src/libImaging/Jpeg2KDecode.c:876`.\n- Reachability: any attacker-controlled JPEG2000 image with many tiles reaches this path during normal `Image.open(...).load()` decoding.\n\n\n### PoC\nThe attached helper script and testcase were used:\n[exercise_j2k_tile_realloc.zip](https://github.com/user-attachments/files/28099912/exercise_j2k_tile_realloc.zip)\n\n\nGenerate the testcase:\n\n```bash\npythonexercise_j2k_tile_realloc.py make poc_3664_rgba_tile1832.jp2 \\\n  --size 3664 --tile 1832\n```\n\nExpected geometry from the helper:\n\n- image size: `3664 x 3664`\n- mode: `RGBA`\n- tile size: `1832 x 1832` (`2x2` tiles)\n- `image_bytes=53699584`\n- uncapped RSS observed:\n  - vulnerable build: `maxrss_kb=180264`\n  - fixed comparison build: `maxrss_kb=138404`\n\nLoad it with the current vulnerable build:\n\n```bash\npython exercise_j2k_tile_realloc.py load poc_3664_rgba_tile1832.jp2\n```\n\nLoad it again under a 160 MB address-space cap:\n\n```bash\npython exercise_j2k_tile_realloc.py load poc_3664_rgba_tile1832.jp2 --limit-mb 160\n```\n\n### Impact\nConservative impact: denial of service through memory exhaustion during JPEG2000 decoding.",
  "id": "GHSA-vjc4-5qp5-m44j",
  "modified": "2026-07-20T23:18:33Z",
  "published": "2026-07-20T23:18:32Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/python-pillow/Pillow/security/advisories/GHSA-vjc4-5qp5-m44j"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-59204"
    },
    {
      "type": "WEB",
      "url": "https://github.com/python-pillow/Pillow/pull/9704"
    },
    {
      "type": "WEB",
      "url": "https://github.com/python-pillow/Pillow/commit/13ada41172142f2fd9f0906f615a00ea623a11ca"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/python-pillow/Pillow"
    },
    {
      "type": "WEB",
      "url": "https://github.com/python-pillow/Pillow/releases/tag/12.3.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Pillow JPEG2000 tiled decode retains a growing scratch buffer and can be used for denial of service"
}



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