GHSA-q6rr-fm2g-g5x8: Scriban Array * Int (ScriptArray<T>.TryEvaluate) Bypasses Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-q6rr-fm2g-g5x8",
  "modified" : "2026-07-06T13:03:57Z",
  "published" : "2026-06-26T21:01:57Z",
  "aliases" : [ ],
  "summary" : "Scriban: array * int (ScriptArray<T>.TryEvaluate) bypasses LoopLimit — incomplete fix for GHSA-c875-h985-hvrc, missed sibling of GHSA-24c8-4792-22hx",
  "details" : "### Summary\n\nThe array multiplication operator (`array * integer`) in Scriban allocates a result whose size is the product of the attacker-controlled integer and the array length, with **no `LoopLimit` / `LimitToString` check and no overflow-safe arithmetic**. A ~40-byte template forces a multi-gigabyte allocation, producing a denial-of-service.\n\nThis is the unguarded sibling of operations that *were* hardened against the same class of abuse: `string * integer` (gated by a `LimitToString` pre-check), `array.insert_at` (gated by `StepLoop`/`LoopLimit` — the **GHSA-24c8-4792-22hx** fix shipped in 7.2.0, scored 8.7 High), and the range/iteration paths covered by **GHSA-c875-h985-hvrc** (\"Built-in operations bypass LoopLimit\", fixed 7.0.0). The same `LoopLimit`-based hardening pattern was applied to those operations but never to `array * integer`.\n\nThis can be observed directly in 7.0.0, the release where GHSA-c875 was patched: `(1..5) * 50000000` (and `1..N | array.size`) correctly throws `Exceeding number of iteration limit '1000'`, while `[1,2,3,4,5] * 50000000` allocates ~2 GB with no limit. The `LoopLimit` control is enforced on the iteration path but not on the `array * int` allocation path, side by side, in the same version. The bug has been present since the operator was introduced in **3.0.0**, survives all of the 6.6.0 / 7.0.0 / 7.2.0 DoS-hardening passes, and is still present in 7.2.0 (current) — i.e. it is both a missed sibling of GHSA-24c8 and an incomplete coverage of GHSA-c875's `LoopLimit` hardening.\n\n### Details\n\nThe `array * int` operator is handled in `ScriptArray<T>.TryEvaluate`:\n\n```csharp\n// src/Scriban/Runtime/ScriptArray.cs:504-508  (Multiply case)\nvar newArray = new ScriptArray<T>(intModifier * array.Count);\nfor (int i = 0; i < intModifier; i++)\n{\n    newArray.AddRange(array);\n}\n```\n\n`intModifier` is the attacker-supplied integer (`context.ToInt(...)`, `ScriptArray.cs:399`). Two problems:\n\n1. **No resource limit.** Neither `new ScriptArray<T>(intModifier * array.Count)` nor the `AddRange` loop consults `LoopLimit`, `LimitToString`, or calls `context.StepLoop(...)`. A grep of the entire `TryEvaluate` method (`ScriptArray.cs:360-560`) finds no `StepLoop` / `LoopLimit` / `Limit` reference. `LoopLimit` (default 1000) is therefore not enforced: a template that requests 250,000,000 elements creates them all without any \"iteration limit\" error.\n\n2. **Integer overflow in the capacity.** `intModifier * array.Count` is unchecked `int` arithmetic. The overflow-safe `long` cast used by the string sibling is absent here.\n\nThe DoS-hardening passes guarded the two sibling operations but not this one:\n\n```csharp\n// src/Scriban/Syntax/Expressions/ScriptBinaryExpression.cs:341  (string * int — GUARDED)\nif (context.LimitToString > 0 && value > 0 && leftText.Length > 0\n        && (long)leftText.Length * value > context.LimitToString)   // long arithmetic, pre-check\n{\n    throw new ScriptRuntimeException(spanMultiplier, $\"String multiplication exceeds LimitToString `{context.LimitToString}`.\");\n}\n```\n\n```csharp\n// src/Scriban/Functions/ArrayFunctions.cs:414  (array.insert_at — GUARDED, GHSA-24c8 fix in 7.2.0)\nfor (int i = array.Count; i < index; i++)\n{\n    context.StepLoop(span, ref loopStep);   // LoopLimit enforced\n    array.Add(null);\n}\n```\n\n`array * int` (`ScriptArray.cs:504`) received neither guard.\n\nWhen the oversized allocation fails as a managed exception, it is wrapped by the binary-expression evaluator:\n\n```csharp\n// src/Scriban/Syntax/Expressions/ScriptBinaryExpression.cs:241-243\ncatch (Exception ex) when (!(ex is ScriptRuntimeException))\n{\n    throw new ScriptRuntimeException(span, ex.Message);\n}\n```\n\nSo a host that wraps `Render()` in `try/catch` sees a `ScriptRuntimeException` carrying the original `OutOfMemoryException` message (or `ArgumentOutOfRangeException` on the integer-overflow path).\n\n### PoC\n\nA single console project reproduces it on the released NuGet package.\n\n`poc.csproj`:\n```xml\n<Project Sdk=\"Microsoft.NET.Sdk\">\n  <PropertyGroup>\n    <OutputType>Exe</OutputType>\n    <TargetFramework>net8.0</TargetFramework>\n    <!-- If only the .NET 9 SDK is installed, change to net9.0. Behavior is identical. -->\n  </PropertyGroup>\n  <ItemGroup>\n    <PackageReference Include=\"Scriban\" Version=\"7.2.0\" />\n  </ItemGroup>\n</Project>\n```\n\n`Program.cs`:\n```csharp\nusing Scriban;\n\n// ~41-byte template requests 5 * 200,000,000 = 1,000,000,000 elements\nstring tpl = \"{{ x = [1,2,3,4,5] * 200000000; x.size }}\";\n\nSystem.Console.WriteLine(\"Rendering...\");\nvar sw = System.Diagnostics.Stopwatch.StartNew();\nvar result = Template.Parse(tpl).Render();           // allocates ~7.7 GB\nSystem.Console.WriteLine($\"size={result.Trim()} peakWS=\"\n    + System.Diagnostics.Process.GetCurrentProcess().PeakWorkingSet64 / (1024 * 1024)\n    + \"MB elapsed=\" + sw.ElapsedMilliseconds + \"ms\");\n```\n\nRun:\n```sh\ndotnet run -c Release\n```\n\nMeasured peak working set on Scriban 7.2.0 (net8.0, .NET 9 runtime, Linux), varying only the multiplier:\n\n| Multiplier | template size | elements | peak working set |\n|---|---|---|---|\n| 100,000 | 38 B | 500K | 49 MB (not a DoS) |\n| 50,000,000 | 40 B | 250M | 1,958 MB |\n| 200,000,000 | 41 B | 1B | 7,681 MB |\n| 400,000,000 | 41 B | 2B | 15,313 MB |\n| 429,496,730 | 41 B | — | integer overflow in `intModifier * array.Count` → wrapped `ArgumentOutOfRangeException` |\n\n`LoopLimit` (default 1000) is demonstrably not enforced: 250,000,000 elements are created with no \"iteration limit\" error. Reproduced identically on released NuGet **6.6.0, 7.0.0, 7.1.0, and 7.2.0**, and on **3.0.0, 4.0.0, 5.0.0, 5.10.0, 6.0.0, 6.2.1, 6.5.8** (~2 GB at multiplier 50,000,000). Version **2.1.4 and earlier are NOT affected** — the operator did not exist (`Unable to convert type ScriptArray to int`).\n\n### Impact\n\n- **Type:** Denial of service via uncontrolled memory allocation (CWE-789 / CWE-1284). The result size is `intModifier * array.Count`, attacker-controlled, with no limit and no overflow-safe arithmetic.\n- **Severity:** 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` = **8.7 (High)** — the same vector and score GitHub/Scriban assigned to the sibling advisory GHSA-24c8-4792-22hx. CVSS 3.1 equivalent `AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H` = **7.5 (High)**.\n- **Who is impacted:** any application that renders a template whose text is wholly or partially attacker-controlled (the documented server-side template scenario), or that passes attacker-controlled strings to `object.eval` / `object.eval_template`. No `MemberFilter` interaction is required — this is a pure language operation.\n- **Outcome (deployment-dependent, stated honestly):** On systems with sufficient memory, the runtime catches the allocation failure and the host sees a `ScriptRuntimeException` wrapping `OutOfMemoryException` (or `ArgumentOutOfRangeException` on the integer-overflow path) — recoverable per request. On systems where the multi-GB allocation exceeds available memory, the OS OOM-killer can terminate the process before the managed exception fires (this outcome is deployment-dependent and was not reproduced in our 20 GB + swap test environment). In all cases, a ~40-byte template forces a multi-GB allocation and seconds of pegged CPU/GC — a real per-request availability degradation and resource amplification.\n- **Why the existing mitigation does not help:** `LoopLimit` (default 1000) is the documented control for unbounded iteration/allocation, but the `array * int` path never consults it, so a defender running default configuration is not protected.\n- **Affected versions:** 3.0.0 – 7.2.0 (every release containing the `array * int` operator). 2.1.4 and earlier are not affected.\n\n### Suggested remediation\n\nApply the same hardening already used on the sibling operations, in `ScriptArray.cs` (Multiply case, `:504-508`):\n\n- **Mirror `array.insert_at`:** call `context.StepLoop(span, ref loopStep)` inside the fill loop so `LoopLimit` is enforced; or\n- **Mirror `string * int`:** pre-check the result size with overflow-safe arithmetic before allocating, e.g. `if (context.LimitToString > 0 && (long)intModifier * array.Count > context.LimitToString) throw new ScriptRuntimeException(...)`, and compute the capacity as `long` (or reject negative/overflowing products) to remove the integer-overflow path.\n\nAdd a regression test that asserts a graceful `ScriptRuntimeException` for a large multiplier (e.g. `[1,2,3,4,5] * 50000000`) rather than allowing the allocation to proceed.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "NuGet",
      "name" : "Scriban"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "3.0.0"
      }, {
        "fixed" : "7.2.1"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 7.2.0"
    }
  }, {
    "package" : {
      "ecosystem" : "NuGet",
      "name" : "Scriban.Signed"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "3.0.0"
      }, {
        "fixed" : "7.2.1"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 7.2.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/scriban/scriban/security/advisories/GHSA-q6rr-fm2g-g5x8"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/scriban/scriban"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-770" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-26T21:01:57Z",
    "nvd_published_at" : null
  }
}