let interprocedural analysis handle source-available extension methods for LogForgingLogMessageSink's

Author: Gregro

csharp/ql/lib/change-notes/2026-03-19-fix-log-forging-extension-methods.md

@@ -1,8 +1,7 @@
 ---
 category: minorAnalysis
 ---
-* The `cs/log-forging` query no longer treats arguments to user-defined extension methods
-  on `ILogger` types as sinks. Instead, taint is tracked interprocedurally through extension
-  method bodies, reducing false positives when extension methods sanitize input internally.
-  Known framework extension methods (`Microsoft.Extensions.Logging.LoggerExtensions`) are
-  now modeled as explicit sinks via Models as Data.
+* The `cs/log-forging` query no longer treats arguments to extension methods with
+  source code on `ILogger` types as sinks. Instead, taint is tracked interprocedurally
+  through extension method bodies, reducing false positives when extension methods
+  sanitize input internally.

csharp/ql/lib/ext/Microsoft.Extensions.Logging.Sinks.model.yml

@@ -10,7 +10,6 @@ private import semmle.code.csharp.frameworks.system.text.RegularExpressions
 private import semmle.code.csharp.security.Sanitizers
 private import semmle.code.csharp.security.dataflow.flowsinks.ExternalLocationSink
 private import semmle.code.csharp.dataflow.internal.ExternalFlow
-private import semmle.code.csharp.commons.Loggers
 
 /**
  * A data flow source for untrusted user input used in log entries.
@@ -54,13 +53,14 @@ private class HtmlSanitizer extends Sanitizer {
 
 /**
  * An argument to a call to a method on a logger class, excluding extension methods
- * which are analyzed interprocedurally.
+ * with source code which are analyzed interprocedurally.
  */
-private class LogForgingLogMessageSink extends Sink {
+private class LogForgingLogMessageSink extends Sink, LogMessageSink {
   LogForgingLogMessageSink() {
-    this.getExpr() = any(LoggerType i).getAMethod().getACall().getAnArgument() or
-    this.getExpr() =
-      any(MethodCall call | call.getQualifier().getType() instanceof LoggerType).getAnArgument()
+    not exists(ExtensionMethodCall mc |
+      this.getExpr() = mc.getAnArgument() and
+      mc.getTarget().fromSource()
+    )
   }
 }
 

csharp/ql/lib/semmle/code/csharp/security/dataflow/LogForgingQuery.qll

@@ -7,17 +7,16 @@
 edges
 | LogForging.cs:18:16:18:23 | access to local variable username : String | LogForging.cs:21:21:21:43 | ... + ... | provenance |  |
 | LogForging.cs:18:16:18:23 | access to local variable username : String | LogForging.cs:31:50:31:72 | ... + ... | provenance |  |
-| LogForging.cs:18:16:18:23 | access to local variable username : String | LogForging.cs:35:26:35:33 | access to local variable username | provenance | Sink:MaD:1 |
+| LogForging.cs:18:16:18:23 | access to local variable username : String | LogForging.cs:35:26:35:33 | access to local variable username | provenance |  |
 | LogForging.cs:18:16:18:23 | access to local variable username : String | LogForging.cs:40:27:40:49 | ... + ... : String | provenance |  |
 | LogForging.cs:18:27:18:49 | access to property QueryString : NameValueCollection | LogForging.cs:18:16:18:23 | access to local variable username : String | provenance |  |
-| LogForging.cs:18:27:18:49 | access to property QueryString : NameValueCollection | LogForging.cs:18:27:18:61 | access to indexer : String | provenance | MaD:2 |
+| LogForging.cs:18:27:18:49 | access to property QueryString : NameValueCollection | LogForging.cs:18:27:18:61 | access to indexer : String | provenance | MaD:1 |
 | LogForging.cs:18:27:18:61 | access to indexer : String | LogForging.cs:18:16:18:23 | access to local variable username : String | provenance |  |
 | LogForging.cs:40:27:40:49 | ... + ... : String | LogForging.cs:59:63:59:69 | message : String | provenance |  |
 | LogForging.cs:59:63:59:69 | message : String | LogForging.cs:61:21:61:27 | access to parameter message | provenance |  |
 | LogForgingAsp.cs:13:32:13:39 | username : String | LogForgingAsp.cs:17:21:17:43 | ... + ... | provenance |  |
 models
-| 1 | Sink: Microsoft.Extensions.Logging; LoggerExtensions; false; LogError; (Microsoft.Extensions.Logging.ILogger,System.String,System.Object[]); ; Argument[1..2]; log-injection; manual |
-| 2 | Summary: System.Collections.Specialized; NameValueCollection; false; get_Item; (System.String); ; Argument[this]; ReturnValue; taint; df-generated |
+| 1 | Summary: System.Collections.Specialized; NameValueCollection; false; get_Item; (System.String); ; Argument[this]; ReturnValue; taint; df-generated |
 nodes
 | LogForging.cs:18:16:18:23 | access to local variable username : String | semmle.label | access to local variable username : String |
 | LogForging.cs:18:27:18:49 | access to property QueryString : NameValueCollection | semmle.label | access to property QueryString : NameValueCollection |