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C#: Fix FPs (and a small FN) in cs/path-injection #237

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Merged
MathiasVP merged 6 commits into from
May 30, 2025
Merged

C#: Fix FPs (and a small FN) in cs/path-injection #237

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b40a437
C#: Small optimization. Avoid a small CP between sinks and states.
MathiasVP May 27, 2025
03e671a
C#: Add a false negative.
MathiasVP May 27, 2025
a2d4c20
C#: Fix FN by blocking flow out of the function call instead of out o…
MathiasVP May 27, 2025
db7119c
C#: Add a false positive.
MathiasVP May 27, 2025
4dfa886
C#: Recognize more path-normalization steps.
MathiasVP May 27, 2025
2186fef
C#: Accept test changes.
MathiasVP May 27, 2025
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43 changes: 38 additions & 5 deletions csharp/ql/lib/semmle/code/csharp/security/dataflow/TaintedPathQuery.qll
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Original file line number Diff line number Diff line change
Expand Up @@ -52,6 +52,40 @@ private class GetFullPathStep extends PathNormalizationStep {
}
}

/** Holds if `e` may evaluate to an absolute path. */
bindingset[e]
pragma[inline_late]
private predicate isAbsolute(Expr e) {
exists(Expr absolute | DataFlow::localExprFlow(absolute, e) |
exists(Call call | absolute = call |
call.getARuntimeTarget()
.hasFullyQualifiedName(["System.Web.HttpServerUtilityBase", "System.Web.HttpRequest"],
"MapPath")
or
call.getARuntimeTarget().hasFullyQualifiedName("System.IO.Path", "GetFullPath")
or
call.getARuntimeTarget().hasFullyQualifiedName("System.IO.Directory", "GetCurrentDirectory")
)
or
exists(PropertyRead read | absolute = read |
read.getTarget().hasFullyQualifiedName("System", "Environment", "CurrentDirectory")
)
)
}

private class PathCombineStep extends PathNormalizationStep {
override predicate isAdditionalFlowStep(DataFlow::Node n1, DataFlow::Node n2) {
exists(Call call |
// The result of `Path.Combine(x, y)` is an absolute path when `x` is an
// absolute path.
call.getARuntimeTarget().hasFullyQualifiedName("System.IO.Path", "Combine") and
isAbsolute(call.getArgument(0)) and
n1.asExpr() = call.getArgument(1) and
n2.asExpr() = call
)
}
}

/**
* A taint-tracking configuration for uncontrolled data in path expression vulnerabilities.
*/
Expand All @@ -64,10 +98,9 @@ private module TaintedPathConfig implements DataFlow::StateConfigSig {
source instanceof Source and state = NotNormalized()
}

predicate isSink(DataFlow::Node sink, FlowState state) {
sink instanceof Sink and
exists(state)
}
predicate isSink(DataFlow::Node sink) { sink instanceof Sink }

predicate isSink(DataFlow::Node sink, FlowState state) { none() }

predicate isAdditionalFlowStep(DataFlow::Node n1, FlowState s1, DataFlow::Node n2, FlowState s2) {
any(PathNormalizationStep step).isAdditionalFlowStep(n1, n2) and
Expand All @@ -78,7 +111,7 @@ private module TaintedPathConfig implements DataFlow::StateConfigSig {
predicate isBarrier(DataFlow::Node node, FlowState state) { node.(Sanitizer).isBarrier(state) }

predicate isBarrierOut(DataFlow::Node node, FlowState state) {
isAdditionalFlowStep(node, state, _, _)
isAdditionalFlowStep(_, state, node, _)
}
}

Expand Down
9 changes: 9 additions & 0 deletions csharp/ql/test/query-tests/Security Features/CWE-022/TaintedPath/TaintedPath.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -61,6 +61,15 @@ public void ProcessRequest(HttpContext ctx)
{
File.ReadAllText(fullPath); // GOOD
}

// This test ensures that we can flow through `Path.GetFullPath` and still get a result.
ctx.Response.Write(File.ReadAllText(path)); // BAD

string absolutePath = ctx.Request.MapPath("~MyTempFile");
string fullPath2 = Path.Combine(absolutePath, path);
if (fullPath2.StartsWith(absolutePath + Path.DirectorySeparatorChar)) {
File.ReadAllText(fullPath2); // GOOD
}
}

public bool IsReusable
Expand Down
5 changes: 5 additions & 0 deletions csharp/ql/test/query-tests/Security Features/CWE-022/TaintedPath/TaintedPath.expected
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Original file line number Diff line number Diff line change
Expand Up @@ -6,18 +6,21 @@
| TaintedPath.cs:36:25:36:31 | access to local variable badPath | TaintedPath.cs:10:23:10:45 | access to property QueryString : NameValueCollection | TaintedPath.cs:36:25:36:31 | access to local variable badPath | This path depends on a $@. | TaintedPath.cs:10:23:10:45 | access to property QueryString | user-provided value |
| TaintedPath.cs:38:49:38:55 | access to local variable badPath | TaintedPath.cs:10:23:10:45 | access to property QueryString : NameValueCollection | TaintedPath.cs:38:49:38:55 | access to local variable badPath | This path depends on a $@. | TaintedPath.cs:10:23:10:45 | access to property QueryString | user-provided value |
| TaintedPath.cs:51:26:51:29 | access to local variable path | TaintedPath.cs:10:23:10:45 | access to property QueryString : NameValueCollection | TaintedPath.cs:51:26:51:29 | access to local variable path | This path depends on a $@. | TaintedPath.cs:10:23:10:45 | access to property QueryString | user-provided value |
| TaintedPath.cs:66:45:66:48 | access to local variable path | TaintedPath.cs:10:23:10:45 | access to property QueryString : NameValueCollection | TaintedPath.cs:66:45:66:48 | access to local variable path | This path depends on a $@. | TaintedPath.cs:10:23:10:45 | access to property QueryString | user-provided value |
edges
| TaintedPath.cs:10:16:10:19 | access to local variable path : String | TaintedPath.cs:12:50:12:53 | access to local variable path | provenance | |
| TaintedPath.cs:10:16:10:19 | access to local variable path : String | TaintedPath.cs:17:51:17:54 | access to local variable path | provenance | |
| TaintedPath.cs:10:16:10:19 | access to local variable path : String | TaintedPath.cs:25:30:25:33 | access to local variable path | provenance | |
| TaintedPath.cs:10:16:10:19 | access to local variable path : String | TaintedPath.cs:31:30:31:33 | access to local variable path | provenance | |
| TaintedPath.cs:10:16:10:19 | access to local variable path : String | TaintedPath.cs:35:16:35:22 | access to local variable badPath : String | provenance | |
| TaintedPath.cs:10:16:10:19 | access to local variable path : String | TaintedPath.cs:51:26:51:29 | access to local variable path | provenance | |
| TaintedPath.cs:10:16:10:19 | access to local variable path : String | TaintedPath.cs:59:44:59:47 | access to local variable path : String | provenance | |
| TaintedPath.cs:10:23:10:45 | access to property QueryString : NameValueCollection | TaintedPath.cs:10:16:10:19 | access to local variable path : String | provenance | |
| TaintedPath.cs:10:23:10:45 | access to property QueryString : NameValueCollection | TaintedPath.cs:10:23:10:53 | access to indexer : String | provenance | MaD:1 |
| TaintedPath.cs:10:23:10:53 | access to indexer : String | TaintedPath.cs:10:16:10:19 | access to local variable path : String | provenance | |
| TaintedPath.cs:35:16:35:22 | access to local variable badPath : String | TaintedPath.cs:36:25:36:31 | access to local variable badPath | provenance | |
| TaintedPath.cs:35:16:35:22 | access to local variable badPath : String | TaintedPath.cs:38:49:38:55 | access to local variable badPath | provenance | |
| TaintedPath.cs:59:44:59:47 | access to local variable path : String | TaintedPath.cs:66:45:66:48 | access to local variable path | provenance | |
models
| 1 | Summary: System.Collections.Specialized; NameValueCollection; false; get_Item; (System.String); ; Argument[this]; ReturnValue; taint; df-generated |
nodes
Expand All @@ -32,4 +35,6 @@ nodes
| TaintedPath.cs:36:25:36:31 | access to local variable badPath | semmle.label | access to local variable badPath |
| TaintedPath.cs:38:49:38:55 | access to local variable badPath | semmle.label | access to local variable badPath |
| TaintedPath.cs:51:26:51:29 | access to local variable path | semmle.label | access to local variable path |
| TaintedPath.cs:59:44:59:47 | access to local variable path : String | semmle.label | access to local variable path : String |
| TaintedPath.cs:66:45:66:48 | access to local variable path | semmle.label | access to local variable path |
subpaths