diff --git a/changelog.d/unreleased/3052.security.md b/changelog.d/unreleased/3052.security.md
new file mode 100644
index 0000000000..a1c3d8dfb0
--- /dev/null
+++ b/changelog.d/unreleased/3052.security.md
@@ -0,0 +1,16 @@
+---
+category: security
+issues:
+  - 3052
+affected:
+  - src/CodeIndex/Indexer/Extensibility/ExtractorPluginRegistry.cs
+  - tests/CodeIndex.Tests/SymbolExtractorConfiguredPatternTests.cs
+---
+
+## English
+
+- **Pattern config loading now avoids newline split arrays (#3052)** — configured extractor YAML is parsed line-by-line from bounded UTF-8 text, avoiding whole-file `Split('\n')` allocations for configs with many tiny lines.
+
+## 日本語
+
+- **pattern config 読み込みで改行 Split 配列を作らないようにしました (#3052)** — configured extractor YAML を上限付き UTF-8 テキストから行ごとに解析し、小さな行が多い config でファイル全体の `Split('\n')` 割り当てを避けるようにしました。
diff --git a/src/CodeIndex/Indexer/Extensibility/ExtractorPluginRegistry.cs b/src/CodeIndex/Indexer/Extensibility/ExtractorPluginRegistry.cs
index 12e3121462..38ce9d2a0b 100644
--- a/src/CodeIndex/Indexer/Extensibility/ExtractorPluginRegistry.cs
+++ b/src/CodeIndex/Indexer/Extensibility/ExtractorPluginRegistry.cs
@@ -430,33 +430,35 @@ private static void TryLoadPatternConfig(string path)
                     return;
             }
 
-            var configLines = TryReadPatternConfigLines(path);
-            if (configLines == null)
+            var configText = TryReadPatternConfigText(path);
+            if (configText == null)
                 return;
 
             var language = string.Empty;
             var extensions = new List<string>();
             var patterns = new List<ConfiguredSymbolExtractor.PatternRule>();
             string? pendingKind = null;
-            foreach (var rawLine in configLines)
+            var remaining = configText.AsSpan();
+            while (TryReadNextPatternConfigLine(ref remaining, out var rawLine))
             {
                 var line = rawLine.Trim();
-                if (line.Length == 0 || line.StartsWith('#'))
+                if (line.Length == 0 || line[0] == '#')
                     continue;
 
+                var itemLine = TrimPatternConfigListMarker(line);
                 if (TryReadScalar(line, "language", out var value))
                 {
                     language = NormalizePluginLanguage(value);
                 }
-                else if (TryReadScalar(line.TrimStart('-').Trim(), "extension", out value))
+                else if (TryReadScalar(itemLine, "extension", out value))
                 {
                     extensions.Add(NormalizePluginExtension(value) ?? value);
                 }
-                else if (TryReadScalar(line.TrimStart('-').Trim(), "kind", out value))
+                else if (TryReadScalar(itemLine, "kind", out value))
                 {
                     pendingKind = value.Trim();
                 }
-                else if (TryReadScalar(line.TrimStart('-').Trim(), "regex", out value) && pendingKind != null)
+                else if (TryReadScalar(itemLine, "regex", out value) && pendingKind != null)
                 {
                     if (patterns.Count >= MaxPatternRulesPerConfig)
                     {
@@ -573,7 +575,7 @@ private static bool TryReservePatternRuleBudget(string path)
         }
     }
 
-    private static IReadOnlyList<string>? TryReadPatternConfigLines(string path)
+    private static string? TryReadPatternConfigText(string path)
     {
         var fileInfo = new FileInfo(path);
         if (!fileInfo.Exists)
@@ -607,11 +609,38 @@ private static bool TryReservePatternRuleBudget(string path)
         if (bytes == null)
             return null;
 
-        var text = Encoding.UTF8.GetString(bytes);
-        return text
-            .Replace("\r\n", "\n", StringComparison.Ordinal)
-            .Replace('\r', '\n')
-            .Split('\n');
+        return Encoding.UTF8.GetString(bytes);
+    }
+
+    private static bool TryReadNextPatternConfigLine(ref ReadOnlySpan<char> remaining, out ReadOnlySpan<char> line)
+    {
+        if (remaining.IsEmpty)
+        {
+            line = default;
+            return false;
+        }
+
+        var lineBreakIndex = remaining.IndexOfAny('\r', '\n');
+        if (lineBreakIndex < 0)
+        {
+            line = remaining;
+            remaining = default;
+            return true;
+        }
+
+        line = remaining[..lineBreakIndex];
+        var nextIndex = lineBreakIndex + 1;
+        if (remaining[lineBreakIndex] == '\r' && nextIndex < remaining.Length && remaining[nextIndex] == '\n')
+            nextIndex++;
+        remaining = remaining[nextIndex..];
+        return true;
+    }
+
+    private static ReadOnlySpan<char> TrimPatternConfigListMarker(ReadOnlySpan<char> line)
+    {
+        while (!line.IsEmpty && line[0] == '-')
+            line = line[1..];
+        return line.Trim();
     }
 
     private static byte[]? TryReadWindowsPatternConfigBytes(string path)
@@ -831,16 +860,32 @@ private struct WindowsFileInformation
         public uint FileIndexLow;
     }
 
-    private static bool TryReadScalar(string line, string key, out string value)
+    private static bool TryReadScalar(ReadOnlySpan<char> line, string key, out string value)
     {
         value = string.Empty;
-        var prefix = key + ":";
-        if (!line.StartsWith(prefix, StringComparison.OrdinalIgnoreCase))
+        if (line.Length <= key.Length || line[key.Length] != ':')
             return false;
-        value = line[prefix.Length..].Trim().Trim('"', '\'').Replace("\\\\", "\\", StringComparison.Ordinal);
+
+        if (!line.StartsWith(key.AsSpan(), StringComparison.OrdinalIgnoreCase))
+            return false;
+
+        var scalar = TrimScalarQuotes(line[(key.Length + 1)..].Trim());
+        if (scalar.IsEmpty)
+            return false;
+
+        value = scalar.ToString().Replace("\\\\", "\\", StringComparison.Ordinal);
         return value.Length > 0;
     }
 
+    private static ReadOnlySpan<char> TrimScalarQuotes(ReadOnlySpan<char> value)
+    {
+        while (!value.IsEmpty && (value[0] == '"' || value[0] == '\''))
+            value = value[1..];
+        while (!value.IsEmpty && (value[^1] == '"' || value[^1] == '\''))
+            value = value[..^1];
+        return value;
+    }
+
     private static void TryLoadPlugin(string pluginPath)
     {
         var fullPath = pluginPath;
diff --git a/tests/CodeIndex.Tests/SymbolExtractorConfiguredPatternTests.cs b/tests/CodeIndex.Tests/SymbolExtractorConfiguredPatternTests.cs
index d7ca2cea55..d08bcab651 100644
--- a/tests/CodeIndex.Tests/SymbolExtractorConfiguredPatternTests.cs
+++ b/tests/CodeIndex.Tests/SymbolExtractorConfiguredPatternTests.cs
@@ -84,6 +84,35 @@ public void Extract_ConfiguredPatternYaml_RejectsInvalidRegexWithDiagnostic()
         }
     }
 
+    [Fact]
+    public void Extract_ConfiguredPatternYaml_ReadsManyLineConfig()
+    {
+        lock (TestConsoleLock.Gate)
+        {
+            var tempDir = Path.Combine(Path.GetTempPath(), $"cdidx_patterns_many_lines_{Guid.NewGuid():N}");
+            try
+            {
+                var commentLines = string.Join("\n", Enumerable.Repeat("#", 4096));
+                WritePatternConfig(
+                    tempDir,
+                    $"{commentLines}\nlanguage: \"toydsl\"\nextensions:\n  - extension: \".toy\"\npatterns:\n  - kind: \"class\"\n    regex: \"^entity (?<name>\\\\w+)\"\n");
+                ExtractorPluginRegistry.ReloadForTests();
+
+                var symbols = SymbolExtractor.Extract(2, "toydsl", "entity Widget", "demo.toy", tempDir);
+
+                var symbol = Assert.Single(symbols);
+                Assert.Equal("class", symbol.Kind);
+                Assert.Equal("Widget", symbol.Name);
+            }
+            finally
+            {
+                ExtractorPluginRegistry.ResetForTests();
+                if (Directory.Exists(tempDir))
+                    Directory.Delete(tempDir, recursive: true);
+            }
+        }
+    }
+
     [Fact]
     public void Extract_ConfiguredPatternYaml_RejectsOversizeConfigWithDiagnostic()
     {