Security Digest · Critical advisory (no CVE assigned)
GHSA-5wr9-m6jw-xx44: Scriban: Sandbox escape due to TypedObjectAccessorcache bypassing MemberFilter after TemplateContext reuse
Summary TemplateContext caches type accessors by Type only, but those accessors are built using the current MemberFilter and MemberRenamer.
CVSS 9.1 Critical GitHub-reviewed · critical
Should you act?
- Only if you depend on one of the packages below, directly or transitively, in a vulnerable version. Check your lockfile with
dotnet list package --vulnerable --include-transitive. - No CVE has been assigned, so it will not appear in CVE-based scanners that ignore GitHub advisories.
npm audit,pip-auditand Dependabot do read GitHub advisories.
Affected packages
| Ecosystem | Package | Vulnerable | First fixed |
|---|---|---|---|
| NuGet | scriban | < 7.0.0 | 7.0.0 |
| NuGet | Scriban.Signed | < 7.0.0 | 7.0.0 |
Details
Summary
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.
Details
The relevant code path is:
- TemplateContext.GetMemberAccessor() caches accessors in memberAccessors by Type in src/Scriban/TemplateContext.cs lines 850–863. - For plain .NET objects, GetMemberAccessorImpl() creates a new TypedObjectAccessor(type, keyComparer, MemberFilter, MemberRenamer) in src/Scriban/TemplateContext.cs lines 909–939. - 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. - Member access later goes through ScriptMemberExpression.GetValue() in src/Scriban/Syntax/Expressions/ScriptMemberExpression.cs lines 67–95, which uses the cached accessor. - TemplateContext.Reset() does not clear memberAccessors in src/Scriban/TemplateContext.cs lines 877–902.
As 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.
This is especially relevant because the Scriban docs explicitly recommend TemplateContext.MemberFilter for indirect .NET object exposure.
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CVSS: 9.1 (v3.1) CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Sources and references
- GitHub Advisory GHSA-5wr9-m6jw-xx44 github.com
- github.com github.com