CVE-2026-41197: Brillig Heap Corruption Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-jj7c-x25r-r8r3",
  "modified" : "2026-04-27T16:29:20Z",
  "published" : "2026-04-21T20:16:09Z",
  "aliases" : [ "CVE-2026-41197" ],
  "summary" : "Brillig: Heap corruption in foreign call results with nested tuple arrays",
  "details" : "## Description\n\nNoir programs can invoke external functions through foreign calls. When compiling to Brillig bytecode, the SSA instructions are processed block-by-block in `BrilligBlock::compile_block()`. When the compiler encounters an `Instruction::Call` with a `Value::ForeignFunction` target, it invokes `codegen_call()` in `brillig_call/code_gen_call.rs`, which dispatches to `convert_ssa_foreign_call()`.\n\nBefore emitting the foreign call opcode, the compiler must pre-allocate memory for any array results the call will return. This happens through `allocate_external_call_results()`, which iterates over the result types. For `Type::Array` results, it delegates to `allocate_foreign_call_result_array()` to recursively allocate memory on the heap for nested arrays.\n\nThe `BrilligArray` struct is the internal representation of a Noir array in Brillig IR. Its `size` field represents the **semi-flattened size**, the total number of memory slots the array occupies, accounting for the fact that composite types like tuples consume multiple slots per element. This size is computed by `compute_array_length()` in `brillig_block_variables.rs`:\n\n```rust\npub(crate) fn compute_array_length(item_typ: &CompositeType, elem_count: usize) -> usize {\n    item_typ.len() * elem_count\n}\n```\n\nFor the **outer** array, `allocate_external_call_results()` correctly uses `define_variable()`, which internally calls `allocate_value_with_type()`. This function applies the formula above, producing the correct semi-flattened size.\n\nHowever, for **nested** arrays, `allocate_foreign_call_result_array()` contains a bug. When it encounters a nested `Type::Array(types, nested_size)`, it calls:\n\n```rust\nType::Array(_, nested_size) => { \n\tlet inner_array = self.brillig_context.allocate_brillig_array(*nested_size as usize);\n\t// ....\n}\n```\n\nThe pattern `Type::Array(_, nested_size)` discards the inner types with `_` and uses only `nested_size`, the **semantic length** of the nested array (the number of logical elements), not the semi-flattened size. For simple element types this works correctly, but for composite element types it under-allocates. Consider a nested array of type `[(u32, u32); 3]`:\n\n-   Semantic length: 3 (three tuples)\n-   Element size: 2 (each tuple has two fields)\n-   Required semi-flattened size: 6 memory slots\n    \n\nThe current code passes `3` to `allocate_brillig_array()`, which then calls `codegen_initialize_array()`. This function allocates `array.size + ARRAY_META_COUNT` slots, only 4 slots instead of the required 7 (6 data + 1 metadata). When the VM executes the foreign call and writes 6 values plus metadata, it overwrites adjacent heap memory.\n\n## Impact\n\nForeign calls returning nested arrays of tuples or other composite types corrupt the Brillig VM heap.\n\n## Recommendation\n\nMultiply the semantic length by the number of element types when allocating nested arrays. Extract the inner types from the pattern and replace the `nested_size` argument to `allocate_brillig_array()` with `types.len() * nested_size` to compute the semi-flattened size. Alternatively, reuse the existing `compute_array_length()` helper function to maintain consistency with outer array allocation.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "crates.io",
      "name" : "brillig"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.0.0-beta.19"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 1.0.0-beta.18"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/noir-lang/noir/security/advisories/GHSA-jj7c-x25r-r8r3"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-41197"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/noir-lang/noir"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/noir-lang/noir/releases/tag/v1.0.0-beta.19"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-131" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-21T20:16:09Z",
    "nvd_published_at" : "2026-04-23T02:16:18Z"
  }
}