CVE-2026-47261: wasmtime-wasi WASI Path_open(TRUNCATE) Bypasses `FilePerms::WRITE` Host Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-2r75-cxrj-cmph",
  "modified" : "2026-07-08T17:35:44Z",
  "published" : "2026-06-05T15:47:02Z",
  "aliases" : [ "CVE-2026-47261" ],
  "summary" : "wasmtime-wasi: WASI path_open(TRUNCATE) bypasses `FilePerms::WRITE` host restriction",
  "details" : "## Summary\n\nIn `wasmtime-wasi`, when a filesystem preopen is given `DirPerms::all()` and `FilePerms::READ` without `FilePerms::WRITE`,  this wasmtime-wasi enforced access control mechanism can be bypassed by using the wasip2 `descriptor.open-at` or wasip1 `path_open` interfaces by opening a file with `OpenFlags::TRUNCATE` oflag only, for example:\n\n```rust\ndir_descriptor.open_at(\n   PathFlags::empty(),\n   FILENAME,\n   OpenFlags::TRUNCATE,\n   DescriptorFlags::READ,\n)\n```\n\n```rust\nwasip1::path_open(\n    dir_fd,\n    0,\n    FILENAME,\n    wasip1::OFLAGS_TRUNC,\n    wasip1::RIGHTS_FD_READ,\n    0,\n    0\n)\n```\n\nThe root cause is that the clause that considered `OpenFlags::TRUNCATE` did not set `open_mode |= OpenMode::WRITE;`, used later in that function for the access control check against `FilePerms` for whether opening that file is permitted. With the bug corrected, these calls to `open-at` and `path_open` fail with `error-code.not-permitted` and `ERRNO_PERM` respectively.\n\nThe bug in `crates/wasi/src/filesystem.rs`, `Dir::open_at`, lines 967–969:\n\n```rust\nif oflags.contains(OpenFlags::TRUNCATE) {\n    opts.truncate(true).write(true);\n}\n```\nand the single line fix is:\n```rust\nif oflags.contains(OpenFlags::TRUNCATE) {\n    opts.truncate(true).write(true);\n    open_mode |= OpenMode::WRITE;\n}\n```\n\nOnly wasmtime-wasi embeddings that use a combination of DirPerms::MUTATE with FilePerms::READ are affected by this bug, e.g. those that use in the `WasiCtxBuilder`:\n```rust\nbuilder.preopened_dir(\"readonly\", \"readonly\", DirPerms::READ | DirPerms::MUTATE, FilePerms::READ);\n```\n\nIn particular, the Wasmtime project's `wasmtime-cli`'s use of wasmtime-wasi is not affected, because it always sets `FilePerms::all()` for all preopens.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "crates.io",
      "name" : "wasmtime-wasi"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "37.0.0"
      }, {
        "fixed" : "44.0.2"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "crates.io",
      "name" : "wasmtime-wasi"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "25.0.0"
      }, {
        "fixed" : "36.0.10"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "crates.io",
      "name" : "wasmtime-wasi"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "24.0.9"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-2r75-cxrj-cmph"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-47261"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/bytecodealliance/wasmtime"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/bytecodealliance/wasmtime/releases/tag/v24.0.9"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/bytecodealliance/wasmtime/releases/tag/v36.0.10"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/bytecodealliance/wasmtime/releases/tag/v44.0.2"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/bytecodealliance/wasmtime/releases/tag/v45.0.0"
  }, {
    "type" : "WEB",
    "url" : "https://rustsec.org/advisories/RUSTSEC-2026-0149.html"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-284" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-05T15:47:02Z",
    "nvd_published_at" : "2026-06-15T21:17:11Z"
  }
}