80 lines
2.1 KiB
Plaintext
80 lines
2.1 KiB
Plaintext
=== How to fix it in .NET
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:canonicalization_function: System.IO.Path.GetFullPath
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include::../../common/fix/code-rationale.adoc[]
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==== Noncompliant code example
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[source,csharp,diff-id=1,diff-type=noncompliant]
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----
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public class ExampleController : Controller
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{
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private static string TargetDirectory = "/path/to/target/directory/";
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public void Example(string filename)
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{
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string path = Path.Combine(TargetDirectory, filename);
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System.IO.File.Delete(path);
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}
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}
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----
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==== Compliant solution
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[source,csharp,diff-id=1,diff-type=compliant]
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----
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public class ExampleController : Controller
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{
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private static string TargetDirectory = "/path/to/target/directory/";
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public void Example(string filename)
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{
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string path = Path.Combine(TargetDirectory, filename);
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string canonicalDestinationPath = Path.GetFullPath(path);
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if (canonicalDestinationPath.StartsWith(TargetDirectory, StringComparison.Ordinal))
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{
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System.IO.File.Delete(canonicalDestinationPath);
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}
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}
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}
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----
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=== How does this work?
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include::../../common/fix/how-does-this-work.adoc[]
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=== Pitfalls
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include::../../common/pitfalls/partial-path-traversal.adoc[]
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For example, the following code is vulnerable to partial path injection. Note
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that the string `TargetDirectory` does not end with a path separator:
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[source, csharp]
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----
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private static string TargetDirectory = "/Users/John";
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public void Example(string filename)
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{
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string canonicalDestinationPath = Path.GetFullPath(filename);
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if (canonicalDestinationPath.StartsWith(TargetDirectory, StringComparison.Ordinal))
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{
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System.IO.File.Delete(canonicalDestinationPath);
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}
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}
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----
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This check can be bypassed because `"/Users/Johnny/file".startsWith("/Users/John")`
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returns `true`. Thus, for validation, `"/Users/John"` should actually be
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`"/Users/John/"`.
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**Warning**: Some functions remove the terminating path separator in their
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return value. +
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The validation code should be tested to ensure that it cannot be impacted by this
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issue.
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https://github.com/aws/aws-sdk-java/security/advisories/GHSA-c28r-hw5m-5gv3[Here is a real-life example of this vulnerability.]
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