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Java: Improve QHelp for java/path-injection to mention less disruptive fixes.

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This commit is contained in:
Max Schaefer
2023-11-13 14:49:54 +00:00
parent 104700f6d3
commit a46a7fadb2
6 changed files with 93 additions and 27 deletions
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16
java/ql/src/Security/CWE/CWE-022/TaintedPath.java
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@@ -2,23 +2,11 @@ public void sendUserFile(Socket sock, String user) {
BufferedReader filenameReader = new BufferedReader(
new InputStreamReader(sock.getInputStream(), "UTF-8"));
String filename = filenameReader.readLine();
// BAD: read from a file using a path controlled by the user
BufferedReader fileReader = new BufferedReader(
new FileReader("/home/" + user + "/" + filename));
// BAD: read from a file without checking its path
BufferedReader fileReader = new BufferedReader(new FileReader(filename));
String fileLine = fileReader.readLine();
while(fileLine != null) {
sock.getOutputStream().write(fileLine.getBytes());
fileLine = fileReader.readLine();
}
}
public void sendUserFileFixed(Socket sock, String user) {
// ...
// GOOD: remove all dots and directory delimiters from the filename before using
String filename = filenameReader.readLine().replaceAll("\\.", "").replaceAll("/", "");
BufferedReader fileReader = new BufferedReader(
new FileReader("/home/" + user + "/" + filename));
// ...
}

35
java/ql/src/Security/CWE/CWE-022/TaintedPath.qhelp
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@@ -13,27 +13,36 @@ such as "..". Such a path may potentially point to any directory on the file sys
</overview>
<recommendation>
<p>Validate user input before using it to construct a file path. Ideally, follow these rules:</p>
<p>Validate user input before using it to construct a file path.</p>
<ul>
<li>Do not allow more than a single "." character.</li>
<li>Do not allow directory separators such as "/" or "\" (depending on the file system).</li>
<li>Do not rely on simply replacing problematic sequences such as "../". For example, after applying this filter to
".../...//" the resulting string would still be "../".</li>
<li>Ideally use a whitelist of known good patterns.</li>
</ul>
<p>The choice of validation depends on the use case.</p>
<p>If you want to allow paths spanning multiple folders, a common strategy is to make sure that the constructed
file path is contained within a safe root folder, for example by checking that the path starts with the root folder.
Additionally, you need to ensure that the path does not contain any ".." components, since these would allow
the path to escape the root folder.</p>
<p>A safer (but more restrictive) option is to use an allow list of safe paths and make sure that
the user input is one of those paths.</p>
</recommendation>
<example>
<p>In this example, a file name is read from a <code>java.net.Socket</code> and then used to access a file in the
user's home directory and send it back over the socket. However, a malicious user could enter a file name which contains special
characters. For example, the string "../../etc/passwd" will result in the code reading the file located at
"/home/[user]/../../etc/passwd", which is the system's password file. This file would then be sent back to the user,
giving them access to all the system's passwords.</p>
<p>In this example, a file name is read from a <code>java.net.Socket</code> and then used to access a file
and send it back over the socket. However, a malicious user could enter a file name anywhere on the file system,
such as "/etc/passwd".</p>
<sample src="TaintedPath.java" />
<p>Simply checking that the path is under a trusted location (such as the user's home directory) is not enough,
however, since the path could contain relative components such as "..". For example, the string
"/home/[user]/../../etc/passwd" starts with the user's home directory, but would still result in the code reading
the file located at "/etc/passwd".</p>
<p>To fix this, we check that the user-provided path does not contain ".." and starts with the user's home directory.</p>
<sample src="TaintedPathGood.java" />
</example>
<references>

14
java/ql/src/Security/CWE/CWE-022/TaintedPathGood.java Normal file
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@@ -0,0 +1,14 @@
public void sendUserFileGood(Socket sock, String user) {
BufferedReader filenameReader = new BufferedReader(
new InputStreamReader(sock.getInputStream(), "UTF-8"));
String filename = filenameReader.readLine();
// GOOD: ensure that the file is in a designated folder in the user's home directory
if (!filePath.contains("..") && filePath.startsWith("/home/" + user + "/public/")) {
BufferedReader fileReader = new BufferedReader(new FileReader(filePath));
String fileLine = fileReader.readLine();
while(fileLine != null) {
sock.getOutputStream().write(fileLine.getBytes());
fileLine = fileReader.readLine();
}
}
}