GHSA-x6m9-38vm-2xhf: Scriban has an authorization bypass due to stale include cache surviving TemplateContext.Reset()

Summary TemplateContext.Reset() claims that a TemplateContext can be reused safely on the same thread, but it does not clear CachedTemplates. If an application pools TemplateContext objects and uses an ITemplateLoader that resolves content per request, tenant, or user, a previously authorized include can be served to later renders without calling TemplateLoader.Load() again. Details The relevant code path is: - TemplateContext.Reset() only clears output, globals, cultures, and source files in src/Scriban/TemplateContext.cs lines 877–902. - CachedTemplates is initialized once and kept on the context in src/Scriban/TemplateContext.cs line 197. - include resolves templates through IncludeFunction.Invoke() in src/Scriban/Functions/IncludeFunction.cs lines 29–43. - IncludeFunction.Invoke() calls TemplateContext.GetOrCreateTemplate() in src/Scriban/TemplateContext.cs lines 1249–1256. - If a template path is already present in CachedTemplates, Scriban returns the cached compiled template and does not call TemplateLoader.Load() again. This becomes a security issue when ITemplateLoader.Load() returns request-dependent content. A first render can prime the cache with an admin-only or tenant-specific template, and later renders on the same reused TemplateContext will receive that stale template even after Reset(). Proof of Concept Setup mkdir scriban-poc1 cd scriban-poc1 dotnet new console --framework net8.0 dotnet add package Scriban --version 6.6.0 Program.cs using Scriban; using Scriban.Parsing; using Scriban.Runtime; var loader = new SwitchingLoader(); var context = new TemplateContext { TemplateLoader = loader, }; var template = Template.Parse("{{ include 'profile' }}"); loader.Content = "admin-only"; Console.WriteLine("first=" + template.Render(context)); context.Reset(); loader.Content = "guest-view"; Console.WriteLine("second=" + template.Render(context)); se