From 2deec1761b903fc88eaff577f16917af9cc85db2 Mon Sep 17 00:00:00 2001
From: Raimund Andree <r.andree@live.com>
Date: Wed, 21 Oct 2026 14:05:51 +0000
Subject: [PATCH] fix(items): reject a -Filter of more than 32,767 characters

An independent review found that a very long -Filter pattern (for
example, a run of 120,000 question marks, or 45,000 asterisks) crashes
the whole host process with an uncatchable StackOverflowException: the
matcher recurses roughly once per character of the pattern, and a long
enough pattern exhausts the stack. A pattern this long serves no
purpose that a shorter one could not also serve, and the review
confirmed that patterns of 32,767 characters or fewer, of any shape
(literal, "?" repeated, "*" repeated, "*?" repeated, "*." repeated),
do not come close to exhausting the stack.

Added `[ValidateLength(0, 32767)]` next to the existing
`[ValidateNotNull]` on -Filter, so that a pattern longer than 32,767
characters is rejected at parameter binding, before it ever reaches
the matcher, with the same `ParameterArgumentValidationError` and
`'Filter'` in the message as the existing null rejection; shorter
values, including an empty one, are unaffected.

Tests (Tests\ItemCmdlets.Tests.ps1, "Get-ChildItem2" > "Recursion, type
filters, and depth"): a -Filter of 32,768 characters now gives
ParameterArgumentValidationError, and one of exactly 32,767 characters
("?" repeated, in a folder with one file) returns the right result
without crashing. The crash itself was confirmed in a disposable child
process (not through the shared Pester harness, to avoid taking that
process down too) with the reviewer's probe
(C:\Temp\ntfs-rc9\review-probes-r3\p9-longpattern.ps1 -N 120000 -Kind
qm): the process terminated with a StackOverflowException before this
fix, and after it, the same probe at the exact boundaries (32,767 and
32,768 characters, every pattern kind the probe offers) neither
crashes nor is accepted past the limit.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: AI Assistant <ai@example.com>
---
 NTFSSecurity/ItemCmdlets/GetChildItem2.cs |  1 +
 Tests/ItemCmdlets.Tests.ps1               | 22 ++++++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/NTFSSecurity/ItemCmdlets/GetChildItem2.cs b/NTFSSecurity/ItemCmdlets/GetChildItem2.cs
index 39d8b21..fd66987 100644
--- a/NTFSSecurity/ItemCmdlets/GetChildItem2.cs
+++ b/NTFSSecurity/ItemCmdlets/GetChildItem2.cs
@@ -44,6 +44,7 @@ namespace NTFSSecurity
 
         [Parameter(Position = 2)]
         [ValidateNotNull]
+        [ValidateLength(0, 32767)]
         public string Filter
         {
             get { return filter; }
diff --git a/Tests/ItemCmdlets.Tests.ps1 b/Tests/ItemCmdlets.Tests.ps1
index 9a15360..5c26da8 100644
--- a/Tests/ItemCmdlets.Tests.ps1
+++ b/Tests/ItemCmdlets.Tests.ps1
@@ -426,6 +426,28 @@ Describe 'Get-ChildItem2' {
                 Should -Throw -ErrorId 'ParameterArgumentValidationError,NTFSSecurity.GetChildItem2' -ExpectedMessage "*'Filter'*"
         }
 
+        It 'Should reject a -Filter of more than 32,767 characters' {
+            $tooLong = '?' * 32768
+            { Get-ChildItem2 -Path $tree -Filter $tooLong -ErrorAction Stop } |
+                Should -Throw -ErrorId 'ParameterArgumentValidationError,NTFSSecurity.GetChildItem2' -ExpectedMessage "*'Filter'*"
+        }
+
+        # A pattern this long is not useful, but the cmdlet must not crash the host: before this test was added, a
+        # pattern of this length (or a long run of asterisks) recursed deep enough in the matcher to raise an
+        # uncatchable StackOverflowException and terminate the process.
+        It 'Should accept a -Filter of exactly 32,767 characters and return the right result' {
+            $folder = New-TestSandboxItem -Sandbox $sandbox -Name 'FilterMaxLength' -Directory
+            $file = Join-Path -Path $folder -ChildPath 'a'
+            Assert-TestSandboxPath -Sandbox $sandbox -Path $file
+            Set-Content -LiteralPath $file -Value 'a'
+            $longest = '?' * 32767
+
+            $result = @(Get-ChildItem2 -Path $folder -Filter $longest -ErrorAction Stop)
+
+            $result | Should -HaveCount 1
+            $result[0].Name | Should -Be 'a'
+        }
+
         It 'Should stop a recursive pipeline without recording an enumeration error' {
             $result = @(Get-ChildItem2 -Path $tree -Recurse -ErrorVariable childErrors -ErrorAction SilentlyContinue | Select-Object -First 1)