ImageSharp: Tiled fax TIFF: tile buffer sized by TileWidth but fax decompressor writes scanlines of ImageWidth — heap OOB write

{
  "id": "db6f34b611c080609c9f8fb5a66f328f23ebd8a1805a280b99f406f5a3f5c7a8",
  "url": "https://osv.dev/vulnerability/GHSA-v76p-62qx-wwq2",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "ImageSharp: Tiled fax TIFF: tile buffer sized by TileWidth but fax decompressor writes scanlines of ImageWidth — heap OOB write",
    "summary": "## Summary When decoding a tiled TIFF with fax compression (T4/T6/MH), `DecodeTilesChunky` allocates each tile buffer from **TileWidth** (`ceil(TileWidth*bpp/8)*TileLength` bytes) but constructs the fax decompressor with **frame.Width**: `TiffDecompressorsFactory` ignores the `isTiled/tileWidth/tileHeight` parameters entirely. The T4/T6/MH decompressors treat the full image width as the scanline length and advance (and really write, via read-modify-write bit ops) `frame.Width` bits per row, with no bounds check against the tile buffer. The very first tile therefore writes linearly out of bounds — about `ImageWidth/8` bytes per row × TileLength rows into a `TileWidth`-sized buffer. With ImageWidth=4,000,000, TileWidth=16, TileLength=16 this writes ~2 MB past a 32-byte buffer and kills the process deterministically; a T6 all-white variant advances the bit offset by >512 MB silently, showing an alarm-free heap-corruption window for the same defect. A crafted file fully controls the OOB length per tile and works with perfectly legal per-row run codes (no overlong runs needed). Verified at commit `5cd4d0d26a82a9549f297a237aea9cf665bddff8` (main; latest release v4.1.0, the supported major). ## Details Root cause: a size mismatch between tile buffer allocation and decompressor width, because the factory drops the tile parameters. - Allocation: [TiffDecoderCore.cs#L792-L794](https://github.com/SixLabors/ImageSharp/blob/5cd4d0d26a82a9549f297a237aea9cf665bddff8/src/ImageSharp/Formats/T",
    "evidence": "osv:GHSA-v76p-62qx-wwq2",
    "products": [
      {
        "name": {
          "value": "ImageSharp",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "4.1.1",
            "evidence": "/affected/0/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "GHSA-v76p-62qx-wwq2",
      "aliases": [
        "CVE-2026-106118",
        "GHSA-v76p-62qx-wwq2"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "3.0.0"
                },
                {
                  "fixed": "4.1.1"
                }
              ]
            }
          ],
          "package": {
            "name": "ImageSharp",
            "purl": "pkg:nuget/ImageSharp",
            "ecosystem": "NuGet"
          },
          "database_specific": {
            "source": "https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/10/GHSA-v76p-62qx-wwq2/GHSA-v76p-62qx-wwq2.json"
          }
        }
      ],
      "modified": "2026-10-07T16:30:04.820251740Z",
      "provider": "osv",
      "references": [
        "https://github.com/SixLabors/ImageSharp/security/advisories/GHSA-v76p-62qx-wwq2",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-106118",
        "https://github.com/SixLabors/ImageSharp/pull/3176",
        "https://github.com/SixLabors/ImageSharp/commit/9ee7d1dd5b62d8c9f16cc755e76828386bc2191f",
        "https://github.com/SixLabors/ImageSharp",
        "https://github.com/SixLabors/ImageSharp/releases/tag/v4.1.1"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-787"
        ],
        "severity": "HIGH",
        "github_reviewed": true,
        "nvd_published_at": "2026-10-06T19:17:42Z",
        "github_reviewed_at": "2026-10-07T16:18:57Z"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-106118",
        "evidence": "/aliases"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/database_specific/severity"
  },
  "source_id": "core-osv",
  "document_id": 95155,
  "published_at": "2026-10-07T16:18:57+00:00"
}