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C#: Improve precision of cs/uncontrolled-format-string. #19271

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Merged
merged 7 commits into from
May 14, 2025
Merged

C#: Improve precision of cs/uncontrolled-format-string. #19271

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c16be43
C#: Convert cs/uncontrolled-format-string tests to use test inline ex…
michaelnebel Apr 10, 2025
3838a7b
C#: Add a testcase for CompositeFormat.Parse for cs/uncontrolled-form…
michaelnebel Apr 10, 2025
133e8d4
C#: Include CompositeFormat.Parse as Format like method.
michaelnebel Apr 10, 2025
c96003f
C#: Update test expected output.
michaelnebel Apr 10, 2025
6cc3c82
C#: Add change note.
michaelnebel Apr 10, 2025
a7ddfe2
C#: Address review comments.
michaelnebel May 12, 2025
3449a34
C#: Address review comments.
michaelnebel May 13, 2025
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28 changes: 26 additions & 2 deletions csharp/ql/lib/semmle/code/csharp/frameworks/Format.qll
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Original file line number Diff line number Diff line change
@@ -233,15 +233,28 @@ class InvalidFormatString extends StringLiteral {
}
}

/**
* A method call to a method that parses a format string, for example a call
* to `string.Format()`.
*/
abstract private class FormatStringParseCallImpl extends MethodCall {
/**
* Gets the expression used as the format string.
*/
abstract Expr getFormatExpr();
}

final class FormatStringParseCall = FormatStringParseCallImpl;

/**
* A method call to a method that formats a string, for example a call
* to `string.Format()`.
*/
class FormatCall extends MethodCall {
class FormatCall extends FormatStringParseCallImpl {
FormatCall() { this.getTarget() instanceof FormatMethod }

/** Gets the expression used as the format string. */
Expr getFormatExpr() { result = this.getArgument(this.getFormatArgument()) }
override Expr getFormatExpr() { result = this.getArgument(this.getFormatArgument()) }

/** Gets the argument number containing the format string. */
int getFormatArgument() { result = this.getTarget().(FormatMethod).getFormatArgument() }
@@ -289,3 +302,14 @@ class FormatCall extends MethodCall {
result = this.getArgument(this.getFirstArgument() + index)
}
}

/**
* A method call to `System.Text.CompositeFormat.Parse`.
*/
class ParseFormatStringCall extends FormatStringParseCallImpl {
ParseFormatStringCall() {
this.getTarget() = any(SystemTextCompositeFormatClass x).getParseMethod()
}

override Expr getFormatExpr() { result = this.getArgument(0) }
}
16 changes: 0 additions & 16 deletions csharp/ql/src/API Abuse/FormatInvalid.ql
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Original file line number Diff line number Diff line change
@@ -16,22 +16,6 @@ import semmle.code.csharp.frameworks.system.Text
import semmle.code.csharp.frameworks.Format
import FormatFlow::PathGraph

abstract class FormatStringParseCall extends MethodCall {
abstract Expr getFormatExpr();
}

class OrdinaryFormatCall extends FormatStringParseCall instanceof FormatCall {
override Expr getFormatExpr() { result = FormatCall.super.getFormatExpr() }
}

class ParseFormatStringCall extends FormatStringParseCall {
ParseFormatStringCall() {
this.getTarget() = any(SystemTextCompositeFormatClass x).getParseMethod()
}

override Expr getFormatExpr() { result = this.getArgument(0) }
}

module FormatInvalidConfig implements DataFlow::ConfigSig {
predicate isSource(DataFlow::Node n) { n.asExpr() instanceof StringLiteral }

2 changes: 1 addition & 1 deletion csharp/ql/src/Security Features/CWE-134/UncontrolledFormatString.ql
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Original file line number Diff line number Diff line change
@@ -20,7 +20,7 @@ module FormatStringConfig implements DataFlow::ConfigSig {
predicate isSource(DataFlow::Node source) { source instanceof ActiveThreatModelSource }

predicate isSink(DataFlow::Node sink) {
sink.asExpr() = any(FormatCall call | call.hasInsertions()).getFormatExpr()
sink.asExpr() = any(FormatStringParseCall call).getFormatExpr()
}
}

4 changes: 4 additions & 0 deletions csharp/ql/src/change-notes/2025-04-10-uncontrolled-format-string.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,4 @@
---
category: minorAnalysis
---
* The precision of the query `cs/uncontrolled-format-string` has been improved. Calls to `System.Text.CompositeFormat.Parse` are now considered a format like method call.
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cc @coadaflorin

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The precision of the query cs/uncontrolled-format-string has been improved.

Something to explain the kind of improvements will make it easier to understand which way it goes, less FNs, or less FPs.

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@coadaflorin : The change note has been updated. Could you check and approve the PR in case the update is acceptable? Just for future reference - may I assume that the consumers of change notes, know about the abbreviations FPs, FNs and TPs or is better to spell them out?

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@coadaflorin coadaflorin May 14, 2025 •
edited
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Thank you for the change! For simplicity let's spell them out. If someone doesn't know what a false positive is, at least they have a chance of finding something if they google it.

4 changes: 2 additions & 2 deletions csharp/ql/test/query-tests/Security Features/CWE-134/ConsoleUncontrolledFormatString.cs
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Original file line number Diff line number Diff line change
@@ -5,9 +5,9 @@ public class Program
{
public static void Main()
{
var format = Console.ReadLine();
var format = Console.ReadLine(); // $ Source

// BAD: Uncontrolled format string.
var x = string.Format(format, 1, 2);
var x = string.Format(format, 1, 2); // $ Alert
}
}
12 changes: 8 additions & 4 deletions csharp/ql/test/query-tests/Security Features/CWE-134/UncontrolledFormatString.cs
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Original file line number Diff line number Diff line change
@@ -1,18 +1,19 @@
using System;
using System.Text;
using System.IO;
using System.Web;

public class TaintedPathHandler : IHttpHandler
{
public void ProcessRequest(HttpContext ctx)
{
String path = ctx.Request.QueryString["page"];
String path = ctx.Request.QueryString["page"]; // $ Source

// BAD: Uncontrolled format string.
String.Format(path, "Do not do this");
String.Format(path, "Do not do this"); // $ Alert

// BAD: Using an IFormatProvider.
String.Format((IFormatProvider)null, path, "Do not do this");
String.Format((IFormatProvider)null, path, "Do not do this"); // $ Alert

// GOOD: Not the format string.
String.Format("Do not do this", path);
@@ -22,13 +23,16 @@ public void ProcessRequest(HttpContext ctx)

// GOOD: Not a formatting call
Console.WriteLine(path);

// BAD: Uncontrolled format string.
CompositeFormat.Parse(path); // $ Alert
}

System.Windows.Forms.TextBox box1;

void OnButtonClicked()
{
// BAD: Uncontrolled format string.
String.Format(box1.Text, "Do not do this");
String.Format(box1.Text, "Do not do this"); // $ Alert
}
}
31 changes: 17 additions & 14 deletions csharp/ql/test/query-tests/Security Features/CWE-134/UncontrolledFormatString.expected
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Original file line number Diff line number Diff line change
@@ -1,17 +1,19 @@
#select
| ConsoleUncontrolledFormatString.cs:11:31:11:36 | access to local variable format | ConsoleUncontrolledFormatString.cs:8:22:8:39 | call to method ReadLine : String | ConsoleUncontrolledFormatString.cs:11:31:11:36 | access to local variable format | This format string depends on $@. | ConsoleUncontrolledFormatString.cs:8:22:8:39 | call to method ReadLine | thisread from stdin |
| UncontrolledFormatString.cs:12:23:12:26 | access to local variable path | UncontrolledFormatString.cs:9:23:9:45 | access to property QueryString : NameValueCollection | UncontrolledFormatString.cs:12:23:12:26 | access to local variable path | This format string depends on $@. | UncontrolledFormatString.cs:9:23:9:45 | access to property QueryString | thisASP.NET query string |
| UncontrolledFormatString.cs:15:46:15:49 | access to local variable path | UncontrolledFormatString.cs:9:23:9:45 | access to property QueryString : NameValueCollection | UncontrolledFormatString.cs:15:46:15:49 | access to local variable path | This format string depends on $@. | UncontrolledFormatString.cs:9:23:9:45 | access to property QueryString | thisASP.NET query string |
| UncontrolledFormatString.cs:32:23:32:31 | access to property Text | UncontrolledFormatString.cs:32:23:32:31 | access to property Text | UncontrolledFormatString.cs:32:23:32:31 | access to property Text | This format string depends on $@. | UncontrolledFormatString.cs:32:23:32:31 | access to property Text | thisTextBox text |
| UncontrolledFormatString.cs:13:23:13:26 | access to local variable path | UncontrolledFormatString.cs:10:23:10:45 | access to property QueryString : NameValueCollection | UncontrolledFormatString.cs:13:23:13:26 | access to local variable path | This format string depends on $@. | UncontrolledFormatString.cs:10:23:10:45 | access to property QueryString | thisASP.NET query string |
| UncontrolledFormatString.cs:16:46:16:49 | access to local variable path | UncontrolledFormatString.cs:10:23:10:45 | access to property QueryString : NameValueCollection | UncontrolledFormatString.cs:16:46:16:49 | access to local variable path | This format string depends on $@. | UncontrolledFormatString.cs:10:23:10:45 | access to property QueryString | thisASP.NET query string |
| UncontrolledFormatString.cs:28:31:28:34 | access to local variable path | UncontrolledFormatString.cs:10:23:10:45 | access to property QueryString : NameValueCollection | UncontrolledFormatString.cs:28:31:28:34 | access to local variable path | This format string depends on $@. | UncontrolledFormatString.cs:10:23:10:45 | access to property QueryString | thisASP.NET query string |
| UncontrolledFormatString.cs:36:23:36:31 | access to property Text | UncontrolledFormatString.cs:36:23:36:31 | access to property Text | UncontrolledFormatString.cs:36:23:36:31 | access to property Text | This format string depends on $@. | UncontrolledFormatString.cs:36:23:36:31 | access to property Text | thisTextBox text |
| UncontrolledFormatStringBad.cs:12:39:12:44 | access to local variable format | UncontrolledFormatStringBad.cs:9:25:9:47 | access to property QueryString : NameValueCollection | UncontrolledFormatStringBad.cs:12:39:12:44 | access to local variable format | This format string depends on $@. | UncontrolledFormatStringBad.cs:9:25:9:47 | access to property QueryString | thisASP.NET query string |
edges
| ConsoleUncontrolledFormatString.cs:8:13:8:18 | access to local variable format : String | ConsoleUncontrolledFormatString.cs:11:31:11:36 | access to local variable format | provenance | |
| ConsoleUncontrolledFormatString.cs:8:22:8:39 | call to method ReadLine : String | ConsoleUncontrolledFormatString.cs:8:13:8:18 | access to local variable format : String | provenance | Src:MaD:1 |
| UncontrolledFormatString.cs:9:16:9:19 | access to local variable path : String | UncontrolledFormatString.cs:12:23:12:26 | access to local variable path | provenance | |
| UncontrolledFormatString.cs:9:16:9:19 | access to local variable path : String | UncontrolledFormatString.cs:15:46:15:49 | access to local variable path | provenance | |
| UncontrolledFormatString.cs:9:23:9:45 | access to property QueryString : NameValueCollection | UncontrolledFormatString.cs:9:16:9:19 | access to local variable path : String | provenance | |
| UncontrolledFormatString.cs:9:23:9:45 | access to property QueryString : NameValueCollection | UncontrolledFormatString.cs:9:23:9:53 | access to indexer : String | provenance | MaD:2 |
| UncontrolledFormatString.cs:9:23:9:53 | access to indexer : String | UncontrolledFormatString.cs:9:16:9:19 | access to local variable path : String | provenance | |
| UncontrolledFormatString.cs:10:16:10:19 | access to local variable path : String | UncontrolledFormatString.cs:13:23:13:26 | access to local variable path | provenance | |
| UncontrolledFormatString.cs:10:16:10:19 | access to local variable path : String | UncontrolledFormatString.cs:16:46:16:49 | access to local variable path | provenance | |
| UncontrolledFormatString.cs:10:16:10:19 | access to local variable path : String | UncontrolledFormatString.cs:28:31:28:34 | access to local variable path | provenance | |
| UncontrolledFormatString.cs:10:23:10:45 | access to property QueryString : NameValueCollection | UncontrolledFormatString.cs:10:16:10:19 | access to local variable path : String | provenance | |
| UncontrolledFormatString.cs:10:23:10:45 | access to property QueryString : NameValueCollection | UncontrolledFormatString.cs:10:23:10:53 | access to indexer : String | provenance | MaD:2 |
| UncontrolledFormatString.cs:10:23:10:53 | access to indexer : String | UncontrolledFormatString.cs:10:16:10:19 | access to local variable path : String | provenance | |
| UncontrolledFormatStringBad.cs:9:16:9:21 | access to local variable format : String | UncontrolledFormatStringBad.cs:12:39:12:44 | access to local variable format | provenance | |
| UncontrolledFormatStringBad.cs:9:25:9:47 | access to property QueryString : NameValueCollection | UncontrolledFormatStringBad.cs:9:16:9:21 | access to local variable format : String | provenance | |
| UncontrolledFormatStringBad.cs:9:25:9:47 | access to property QueryString : NameValueCollection | UncontrolledFormatStringBad.cs:9:25:9:61 | access to indexer : String | provenance | MaD:2 |
@@ -23,12 +25,13 @@ nodes
| ConsoleUncontrolledFormatString.cs:8:13:8:18 | access to local variable format : String | semmle.label | access to local variable format : String |
| ConsoleUncontrolledFormatString.cs:8:22:8:39 | call to method ReadLine : String | semmle.label | call to method ReadLine : String |
| ConsoleUncontrolledFormatString.cs:11:31:11:36 | access to local variable format | semmle.label | access to local variable format |
| UncontrolledFormatString.cs:9:16:9:19 | access to local variable path : String | semmle.label | access to local variable path : String |
| UncontrolledFormatString.cs:9:23:9:45 | access to property QueryString : NameValueCollection | semmle.label | access to property QueryString : NameValueCollection |
| UncontrolledFormatString.cs:9:23:9:53 | access to indexer : String | semmle.label | access to indexer : String |
| UncontrolledFormatString.cs:12:23:12:26 | access to local variable path | semmle.label | access to local variable path |
| UncontrolledFormatString.cs:15:46:15:49 | access to local variable path | semmle.label | access to local variable path |
| UncontrolledFormatString.cs:32:23:32:31 | access to property Text | semmle.label | access to property Text |
| UncontrolledFormatString.cs:10:16:10:19 | access to local variable path : String | semmle.label | access to local variable path : String |
| UncontrolledFormatString.cs:10:23:10:45 | access to property QueryString : NameValueCollection | semmle.label | access to property QueryString : NameValueCollection |
| UncontrolledFormatString.cs:10:23:10:53 | access to indexer : String | semmle.label | access to indexer : String |
| UncontrolledFormatString.cs:13:23:13:26 | access to local variable path | semmle.label | access to local variable path |
| UncontrolledFormatString.cs:16:46:16:49 | access to local variable path | semmle.label | access to local variable path |
| UncontrolledFormatString.cs:28:31:28:34 | access to local variable path | semmle.label | access to local variable path |
| UncontrolledFormatString.cs:36:23:36:31 | access to property Text | semmle.label | access to property Text |
| UncontrolledFormatStringBad.cs:9:16:9:21 | access to local variable format : String | semmle.label | access to local variable format : String |
| UncontrolledFormatStringBad.cs:9:25:9:47 | access to property QueryString : NameValueCollection | semmle.label | access to property QueryString : NameValueCollection |
| UncontrolledFormatStringBad.cs:9:25:9:61 | access to indexer : String | semmle.label | access to indexer : String |
4 changes: 3 additions & 1 deletion csharp/ql/test/query-tests/Security Features/CWE-134/UncontrolledFormatString.qlref
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Original file line number Diff line number Diff line change
@@ -1,2 +1,4 @@
query: Security Features/CWE-134/UncontrolledFormatString.ql
postprocess: utils/test/PrettyPrintModels.ql
postprocess:
- utils/test/PrettyPrintModels.ql
- utils/test/InlineExpectationsTestQuery.ql
4 changes: 2 additions & 2 deletions csharp/ql/test/query-tests/Security Features/CWE-134/UncontrolledFormatStringBad.cs
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Original file line number Diff line number Diff line change
@@ -6,9 +6,9 @@ public class HttpHandler : IHttpHandler

public void ProcessRequest(HttpContext ctx)
{
string format = ctx.Request.QueryString["nameformat"];
string format = ctx.Request.QueryString["nameformat"]; // $ Source

// BAD: Uncontrolled format string.
FormattedName = string.Format(format, Surname, Forenames);
FormattedName = string.Format(format, Surname, Forenames); // $ Alert
}
}