98 lines
2.9 KiB
Plaintext
98 lines
2.9 KiB
Plaintext
== How to fix it in Java SE
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=== Code examples
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:canonicalization_function1: java.io.File.getCanonicalFile
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:canonicalization_function2: java.io.File.getCanonicalPath
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include::../../common/fix/code-rationale.adoc[]
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==== Noncompliant code example
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[source,java,diff-id=1,diff-type=noncompliant]
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----
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public class Example {
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static private String targetDirectory = "/example/directory/";
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public void ExtractEntry(ZipFile zipFile) throws IOException {
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Enumeration<? extends ZipEntry> entries = zipFile.entries();
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ZipEntry entry = entries.nextElement();
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InputStream inputStream = zipFile.getInputStream(entry);
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File file = new File(targetDirectory + entry.getName());
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Files.copy(inputStream, file.toPath(), StandardCopyOption.REPLACE_EXISTING);
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}
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}
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----
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==== Compliant solution
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[source,java,diff-id=1,diff-type=compliant]
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----
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public class Example {
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static private String targetDirectory = "/example/directory/";
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public void ExtractEntry(ZipFile zipFile) throws IOException {
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Enumeration<? extends ZipEntry> entries = zipFile.entries();
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ZipEntry entry = entries.nextElement();
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InputStream inputStream = zipFile.getInputStream(entry);
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File file = new File(targetDirectory + entry.getName());
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String canonicalDestinationPath = file.getCanonicalPath();
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if (canonicalDestinationPath.startsWith(targetDirectory)) {
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Files.copy(inputStream, file.toPath(), StandardCopyOption.REPLACE_EXISTING, LinkOption.NOFOLLOW_LINKS);
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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, java]
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----
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static private String targetDirectory = "/Users/John";
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public void ExtractEntry(ZipFile zipFile) throws IOException {
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Enumeration<? extends ZipEntry> entries = zipFile.entries();
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ZipEntry entry = entries.nextElement();
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InputStream inputStream = zipFile.getInputStream(entry);
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File file = new File(entry.getName());
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String canonicalDestinationPath = file.getCanonicalPath();
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if (canonicalDestinationPath.startsWith(targetDirectory)) {
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Files.copy(inputStream, file.toPath(), StandardCopyOption.REPLACE_EXISTING, LinkOption.NOFOLLOW_LINKS);
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}
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}
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----
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This check can be bypassed because `"/Users/Johnny".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, such as `.getCanonicalPath`, remove the
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terminating path separator in their 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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