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Merge pull request #14793 from github/max-schaefer/tainted-path-qhelp

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Java: Improve QHelp for `java/path-injection` to mention less disruptive fixes.
This commit is contained in:
Max Schaefer
2023-11-16 14:09:55 +00:00
committed by GitHub
parent 69ab389d9f a5e7ef424e
commit ca334021ad
6 changed files with 97 additions and 28 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));
// ...
}

40
java/ql/src/Security/CWE/CWE-022/TaintedPath.qhelp
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@@ -8,32 +8,44 @@ can result in sensitive information being revealed or deleted, or an attacker be
behavior by modifying unexpected files.</p>
<p>Paths that are naively constructed from data controlled by a user may contain unexpected special characters,
such as "..". Such a path may potentially point to any directory on the file system.</p>
such as "..". Such a path may potentially point anywhere on the file system.</p>
</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 whether you want to allow the user to specify complex paths with
multiple components that may span multiple folders, or only simple filenames without a path component.</p>
<p>In the former case, 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 otherwise
even a path that starts with the root folder could be used to access files outside the root folder.</p>
<p>In the latter case, if you want to ensure that the user input is interpreted as a simple filename without
a path component, you can remove all path separators ("/" or "\") and all ".." sequences from the input
before using it to construct a file path. Note that it is <i>not</i> sufficient to only remove "../" sequences:
for example, applying this filter to ".../...//" would still result in the string "../".</p>
<p>Finally, the simplest (but most restrictive) option is to use an allow list of safe patterns and make sure that
the user input matches one of these patterns.</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 a known public folder) is not enough,
however, since the path could contain relative components such as "..". To fix this, check that it does
not contain ".." and starts with the public folder.</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 (!filename.contains("..") && filename.startsWith("/home/" + user + "/public/")) {
BufferedReader fileReader = new BufferedReader(new FileReader(filename));
String fileLine = fileReader.readLine();
while(fileLine != null) {
sock.getOutputStream().write(fileLine.getBytes());
fileLine = fileReader.readLine();
}
}
}

12
java/ql/test/query-tests/security/CWE-022/semmle/tests/TaintedPath.expected
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@@ -1,4 +1,9 @@
edges
| TaintedPath.java:11:38:11:110 | new BufferedReader(...) : BufferedReader | TaintedPath.java:12:24:12:37 | filenameReader : BufferedReader |
| TaintedPath.java:11:57:11:109 | new InputStreamReader(...) : InputStreamReader | TaintedPath.java:11:38:11:110 | new BufferedReader(...) : BufferedReader |
| TaintedPath.java:11:79:11:99 | getInputStream(...) : InputStream | TaintedPath.java:11:57:11:109 | new InputStreamReader(...) : InputStreamReader |
| TaintedPath.java:12:24:12:37 | filenameReader : BufferedReader | TaintedPath.java:12:24:12:48 | readLine(...) : String |
| TaintedPath.java:12:24:12:48 | readLine(...) : String | TaintedPath.java:14:68:14:75 | filename |
| Test.java:19:18:19:38 | getHostName(...) : String | Test.java:24:20:24:23 | temp |
| Test.java:19:18:19:38 | getHostName(...) : String | Test.java:27:21:27:24 | temp |
| Test.java:19:18:19:38 | getHostName(...) : String | Test.java:30:44:30:47 | temp |
@@ -184,6 +189,12 @@ edges
| mad/Test.java:221:26:221:33 | source(...) : String | mad/Test.java:221:19:221:33 | (...)... |
| mad/Test.java:226:29:226:36 | source(...) : String | mad/Test.java:226:20:226:36 | (...)... |
nodes
| TaintedPath.java:11:38:11:110 | new BufferedReader(...) : BufferedReader | semmle.label | new BufferedReader(...) : BufferedReader |
| TaintedPath.java:11:57:11:109 | new InputStreamReader(...) : InputStreamReader | semmle.label | new InputStreamReader(...) : InputStreamReader |
| TaintedPath.java:11:79:11:99 | getInputStream(...) : InputStream | semmle.label | getInputStream(...) : InputStream |
| TaintedPath.java:12:24:12:37 | filenameReader : BufferedReader | semmle.label | filenameReader : BufferedReader |
| TaintedPath.java:12:24:12:48 | readLine(...) : String | semmle.label | readLine(...) : String |
| TaintedPath.java:14:68:14:75 | filename | semmle.label | filename |
| Test.java:19:18:19:38 | getHostName(...) : String | semmle.label | getHostName(...) : String |
| Test.java:24:20:24:23 | temp | semmle.label | temp |
| Test.java:27:21:27:24 | temp | semmle.label | temp |
@@ -375,6 +386,7 @@ nodes
| mad/Test.java:226:29:226:36 | source(...) : String | semmle.label | source(...) : String |
subpaths
#select
| TaintedPath.java:14:53:14:76 | new FileReader(...) | TaintedPath.java:11:79:11:99 | getInputStream(...) : InputStream | TaintedPath.java:14:68:14:75 | filename | This path depends on a $@. | TaintedPath.java:11:79:11:99 | getInputStream(...) | user-provided value |
| Test.java:24:11:24:24 | new File(...) | Test.java:19:18:19:38 | getHostName(...) : String | Test.java:24:20:24:23 | temp | This path depends on a $@. | Test.java:19:18:19:38 | getHostName(...) | user-provided value |
| Test.java:27:11:27:25 | get(...) | Test.java:19:18:19:38 | getHostName(...) : String | Test.java:27:21:27:24 | temp | This path depends on a $@. | Test.java:19:18:19:38 | getHostName(...) | user-provided value |
| Test.java:30:11:30:48 | getPath(...) | Test.java:19:18:19:38 | getHostName(...) : String | Test.java:30:44:30:47 | temp | This path depends on a $@. | Test.java:19:18:19:38 | getHostName(...) | user-provided value |

35
java/ql/test/query-tests/security/CWE-022/semmle/tests/TaintedPath.java Normal file
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@@ -0,0 +1,35 @@
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.InputStreamReader;
import java.net.Socket;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.io.IOException;
public class TaintedPath {
public void sendUserFile(Socket sock, String user) throws IOException {
BufferedReader filenameReader = new BufferedReader(new InputStreamReader(sock.getInputStream(), "UTF-8"));
String filename = filenameReader.readLine();
// 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 sendUserFileGood(Socket sock, String user) throws IOException {
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 (!filename.contains("..") && filename.startsWith("/home/" + user + "/public/")) {
BufferedReader fileReader = new BufferedReader(new FileReader(filename));
String fileLine = fileReader.readLine();
while(fileLine != null) {
sock.getOutputStream().write(fileLine.getBytes());
fileLine = fileReader.readLine();
}
}
}
}

8
java/ql/test/query-tests/security/CWE-022/semmle/tests/Test.java
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@@ -101,4 +101,12 @@ class Test {
new File(new URI(null, null, null, 0, t, null, null));
}
void doGet6(String root, InetAddress address)
throws IOException{
String temp = address.getHostName();
// GOOD: Use `contains` and `startsWith` to check if the path is safe
if (!temp.contains("..") && temp.startsWith(root + "/")) {
File file = new File(temp);
}
}
}