CVE-2026-59204: Pillow Denial of Service Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-vjc4-5qp5-m44j",
  "modified" : "2026-07-20T23:18:33Z",
  "published" : "2026-07-20T23:18:32Z",
  "aliases" : [ "CVE-2026-59204" ],
  "summary" : "Pillow JPEG2000 tiled decode retains a growing scratch buffer and can be used for denial of service",
  "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->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.\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->buffer` 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.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "pillow"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "8.2.0"
      }, {
        "fixed" : "12.3.0"
      } ]
    } ]
  } ],
  "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"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-770", "CWE-789" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-20T23:18:32Z",
    "nvd_published_at" : "2026-07-14T16:17:02Z"
  }
}