GHSA-p6q4-fgr8-vx4p: 
C# vulnerability analysis and mitigation

Summary

StackOverflowException via nested array initializers bypasses ExpressionDepthLimit fix (GHSA-wgh7-7m3c-fx25)

Details

The recent fix for GHSA-wgh7-7m3c-fx25 (uncontrolled recursion in parser) added ExpressionDepthLimit defaulting to 250. However, deeply nested array initializers ([[[[...) recurse through ParseArrayInitializer → ParseExpression → ParseArrayInitializer, which is a different recursion path not covered by the expression depth counter. This causes a StackOverflowException on current main (commit b5ac4bf - "Add limits for default safety").

PoC

using Scriban;
// ExpressionDepthLimit (default 250) does NOT prevent this crash
string nested = "{{ " + new string('[', 5000) + "1" + new string(']', 5000) + " }}";
Template.Parse(nested); // StackOverflowException - process terminates

Impact

Same as GHSA-wgh7-7m3c-fx25: High severity. StackOverflowException cannot be caught with try/catch in .NET - the process terminates immediately. Any application calling Template.Parse with untrusted input is vulnerable, even with the new default ExpressionDepthLimit enabled.