CVE-2021-23899: Improper Restriction of XML External Entity Reference (CWE-611)
value: OWASP json-sanitizer before 1.2.2 may emit closing SCRIPT tags and CDATA section delimiters for crafted input. This allows an attacker to inject arbitrary HTML or XML into embedding documents.
CWE description: The product processes an XML document that can contain XML entities with URIs that resolve to documents outside of the intended sphere of control, causing the product to embed incorrect documents into its output.
CVSS v3 base score: 9.8
Published: 2021-01-13T16:15Z
Repository: https://github.com/OWASP/json-sanitizer
Language: Java
Files changed: src/test/java/com/google/json/FuzzyTest.java, src/test/java/com/google/json/JsonSanitizerTest.java
Commit date: 2021-01-12 17:31:19 -0500
Commit message: Tests for fixes for previously undisclosed vulnerabilities

These include tests that reproduced fuzzer findings cqommunicated
privately by Fabian Meumertzheim of codeintelligence.

They were held back, separate from the fixes, until a release had time
to propagate.

Public disclosure at
https://groups.google.com/g/json-sanitizer-support/c/dAW1AeNMoA0

Diff: diff --git a/src/test/java/com/google/json/FuzzyTest.java b/src/test/java/com/google/json/FuzzyTest.java
index 1bce387..2bd9131 100644
--- a/src/test/java/com/google/json/FuzzyTest.java
+++ b/src/test/java/com/google/json/FuzzyTest.java
@@ -60,10 +60,36 @@ public final class FuzzyTest extends TestCase {
     for (String fuzzyWuzzyString : new FuzzyStringGenerator(rnd)) {
       try {
         String sanitized0 = JsonSanitizer.sanitize(fuzzyWuzzyString);
         String sanitized1 = JsonSanitizer.sanitize(sanitized0);
         // Test idempotence.
+        if (!sanitized0.equals(sanitized1)) {
+          int commonPrefixLen = 0;
+          int minLength = Math.min(sanitized0.length(), sanitized1.length());
+          while (commonPrefixLen < minLength) {
+            if (sanitized0.charAt(commonPrefixLen) != sanitized1.charAt(commonPrefixLen)) {
+              break;
+            }
+            ++commonPrefixLen;
+          }
+
+          int right0 = sanitized0.length();
+          int right1 = sanitized1.length();
+          while (right0 > commonPrefixLen && right1 > commonPrefixLen) {
+            if (sanitized0.charAt(right0 - 1) != sanitized1.charAt(right1 - 1)) {
+              break;
+            }
+            --right0;
+            --right1;
+          }
+
+          int commonSuffixLen = sanitized0.length() - right0;
+
+          System.err.println("Difference at " + commonPrefixLen + " to -" + commonSuffixLen);
+          System.err.println("Before: " + excerpt(sanitized0, commonPrefixLen, right0));
+          System.err.println("After:  " + excerpt(sanitized0, commonPrefixLen, right1));
+        }
         assertEquals(fuzzyWuzzyString + "  =>  " + sanitized0, sanitized0,
                      sanitized1);
       } catch (Throwable th) {
         System.err.println("Failed on `" + fuzzyWuzzyString + "`");
         hexDump(fuzzyWuzzyString.getBytes("UTF16"), System.err);
@@ -88,10 +114,27 @@ public final class FuzzyTest extends TestCase {
       byte b = bytes[i];
       app.append("0123456789ABCDEF".charAt((b >>> 4) & 0xf));
       app.append("0123456789ABCDEF".charAt((b >>> 0) & 0xf));
     }
   }
+
+  private static String excerpt(String s, int left, int right) {
+    int leftIncl = left - 10;
+    boolean ellipseLeft = leftIncl > 0;
+    if (!ellipseLeft) { leftIncl = 0; }
+
+    int rightIncl = right + 10;
+    boolean ellipseRight = s.length() > rightIncl;
+    if (!ellipseRight) {
+      rightIncl = s.length();
+    }
+
+    return s.substring(leftIncl, rightIncl)
+            .replace("\r", "\\r")
+            .replace("\n", "\\n")
+            .replace("\\", "\\\\");
+  }
 }
 
 final class FuzzyStringGenerator implements Iterable<String> {
   final Random rnd;
 
diff --git a/src/test/java/com/google/json/JsonSanitizerTest.java b/src/test/java/com/google/json/JsonSanitizerTest.java
index 073ab22..5020533 100644
--- a/src/test/java/com/google/json/JsonSanitizerTest.java
+++ b/src/test/java/com/google/json/JsonSanitizerTest.java
@@ -14,10 +14,12 @@
 
 package com.google.json;
 
 import static com.google.json.JsonSanitizer.DEFAULT_NESTING_DEPTH;
 import static com.google.json.JsonSanitizer.sanitize;
+
+import java.util.Locale;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 import junit.framework.TestCase;
 import org.junit.Test;
 
@@ -196,11 +198,11 @@ public final class JsonSanitizerTest extends TestCase {
     assertEquals(1, new JsonSanitizer("", Integer.MIN_VALUE).getMaximumNestingDepth());
     assertEquals(JsonSanitizer.MAXIMUM_NESTING_DEPTH, new JsonSanitizer("", Integer.MAX_VALUE).getMaximumNestingDepth());
   }
 
   @Test
-  public static final void testClosedArray() {
+  public static final void testUnopenedArray() {
     // Discovered by fuzzer with seed -Dfuzz.seed=df3b4778ce54d00a
     assertSanitized("-1742461140214282", "\ufeff-01742461140214282]");
   }
 
   @Test
@@ -226,6 +228,104 @@ public final class JsonSanitizerTest extends TestCase {
     assertSanitized("\"--\\u003e\"", "\"-->\"");
     assertSanitized("-0", "-->");
 
     assertSanitized("\"\\u003c!--\\u003cscript>\"", "\"<!--<script>\"");
   }
+
+  @Test
+  public static final void testLongOctalNumberWithBadDigits() {
+    // Found by Fabian Meumertzheim using CI Fuzz (https://www.code-intelligence.com)
+    assertEquals(
+            "-888888888888888888888",
+            JsonSanitizer.sanitize("-0888888888888888888888")
+    );
+  }
+
+  @Test
+  public static final void testLongNumberInUnclosedInputWithU80() {
+    // Found by Fabian Meumertzheim using CI Fuzz (https://www.code-intelligence.com)
+    assertEquals(
+            "{\"\":{\"\":{\"\":{\"\":{\"\":{\"\":{\"x80\":{\"\":{\"\":[-400557869725698078427]}}}}}}}}}",
+            JsonSanitizer.sanitize("{{{{{{{\\x80{{([-053333333304233333333333")
+    );
+  }
+
+  @Test
+  public static final void testSlashFour() {
+    // Found by Fabian Meumertzheim using CI Fuzz (https://www.code-intelligence.com)
+    assertEquals("\"y\\u0004\"", JsonSanitizer.sanitize("y\\4")); // "y\4"
+  }
+
+  @Test
+  public static final void testUnterminatedObject() {
+    // Found by Fabian Meumertzheim using CI Fuzz (https://www.code-intelligence.com)
+    String input = "?\u0000\u0000\u0000{{\u0000\ufffd\u0003]ve{R]\u00000\ufffd\u0016&e{\u0003]\ufffda<!.b<!<!cc1x\u0000\u00005{281<\u0000.{t\u0001\ufffd5\ufffd{5\ufffd\ufffd0\ufffd15\r\ufffd\u0000\u0000\u0000~~-0081273222428822883223759,55\ufffd\u0000\ufffd\t\u0000\ufffd";
+    String got = JsonSanitizer.sanitize(input);
+    String want = "{\"\":{},\"ve\":{\"R\":null},\"0\":\"e\",\"\":{},\"a<!.b<!<!cc1x\":5,\"\":{\"281\":0.0,\"\":{\"t\":5,\"\":{\"5\":0,\"15\"\r:-81273222428822883223759,\"55\"\t:null}}}}";
+    assertEquals(want, got);
+  }
+
+  @Test
+  public static final void testCrash1() {
+    // Found by Fabian Meumertzheim using CI Fuzz (https://www.code-intelligence.com)
+    String input = "?\u0000\u0000\u0000{{\u0000\ufffd\u0003]ve{R]\u00000\ufffd\ufffd\u0016&e{\u0003]\ufffda<!.b<!<!c\u00005{281<\u0000.{t\u0001\ufffd5\ufffd{515\r[\u0000\u0000\u0000~~-008127322242\ufffd\ufffd\ufffd\ufffd\ufffd\ufffd\ufffd\ufffd23759,551x\u0000\u00006{281<\u0000.{t\u0001\ufffd5\ufffd{5\ufffd\ufffd0\ufffd15\r[\u0000\u0000\u0000~~-0081273222428822883223759,\ufffd";
+    String want = "{\"\":{},\"ve\":{\"R\":null},\"0\":\"e\",\"\":{},\"a<!.b<!<!c\":5,\"\":{\"281\":0.0,\"\":{\"t\":5,\"\":{\"515\"\r:[-8127322242,23759,551,6,{\"281\":0.0,\"\":{\"t\":5,\"\":{\"5\":0,\"15\"\r:[-81273222428822883223759]}}}]}}}}";
+    String got = JsonSanitizer.sanitize(input);
+    assertEquals(want, got);
+  }
+
+  @Test
+  public static final void testDisallowedSubstrings() {
+    // Found by Fabian Meumertzheim using CI Fuzz (https://www.code-intelligence.com)
+    String[] inputs = {
+            "x<\\script>",
+            "x</\\script>",
+            "x</sc\\ript>",
+            "x<\\163cript>",
+            "x</\\163cript>",
+            "x<\\123cript>",
+            "x</\\123cript>",
+            "u\\u\\uu\ufffd\ufffd\\u7u\\u\\u\\u\ufffdu<\\script>5",
+            "z\\<\\!--",
+            "z\\<!\\--",
+            "z\\<!-\\-",
+            "z\\<\\!--",
+            "\"\\]]\\>",
+    };
+    for (String input : inputs) {
+      String out = JsonSanitizer.sanitize(input).toLowerCase(Locale.ROOT);
+      assertFalse(out, out.contains("<!--"));
+      assertFalse(out, out.contains("-->"));
+      assertFalse(out, out.contains("<script"));
+      assertFalse(out, out.contains("</script"));
+      assertFalse(out, out.contains("]]>"));
+      assertFalse(out, out.contains("<![cdata["));
+    }
+  }
+
+  @Test
+  public static final void testXssPayload() {
+    // Found by Fabian Meumertzheim using CI Fuzz (https://www.code-intelligence.com)
+    String input = "x</\\script>u\\u\\uu\ufffd\ufffd\\u7u\\u\\u\\u\ufffdu<\\script>5+alert(1)//";
+    assertEquals(
+            "\"x\\u003c/script>uuuu\uFFFD\uFFFDu7uuuu\uFFFDu\\u003cscript>5+alert(1)//\"",
+            JsonSanitizer.sanitize(input)
+    );
+  }
+
+  @Test
+  public static final void testInvalidOutput() {
+    // Found by Fabian Meumertzheim using CI Fuzz (https://www.code-intelligence.com)
+    String input = "\u0010{'\u0000\u0000'\"\u0000\"{.\ufffd-0X29295909049550970,\n\n0";
+    String want = "{\"\\u0000\\u0000\":\"\\u0000\",\"\":{\"0\":-47455995597866469744,\n\n\"0\":null}}";
+    String got = JsonSanitizer.sanitize(input);
+    assertEquals(want, got);
+  }
+
+  @Test
+  public static final void testBadNumber() {
+    String input = "¶0x.\\蹃4\\À906";
+    String want = "0.0";
+    String got = JsonSanitizer.sanitize(input);
+    assertEquals(want, got);
+  }
 }

Vulnerable code:   public static final void testClosedArray() {
Fixed code:         if (!sanitized0.equals(sanitized1)) {
          int commonPrefixLen = 0;
          int minLength = Math.min(sanitized0.length(), sanitized1.length());
          while (commonPrefixLen < minLength) {
            if (sanitized0.charAt(commonPrefixLen) != sanitized1.charAt(commonPrefixLen)) {
              break;
            }
            ++commonPrefixLen;
          }

          int right0 = sanitized0.length();
          int right1 = sanitized1.length();
          while (right0 > commonPrefixLen && right1 > commonPrefixLen) {
            if (sanitized0.charAt(right0 - 1) != sanitized1.charAt(right1 - 1)) {
              break;
            }
            --right0;
            --right1;
          }

          int commonSuffixLen = sanitized0.length() - right0;

          System.err.println("Difference at " + commonPrefixLen + " to -" + commonSuffixLen);
          System.err.println("Before: " + excerpt(sanitized0, commonPrefixLen, right0));
          System.err.println("After:  " + excerpt(sanitized0, commonPrefixLen, right1));
        }

  private static String excerpt(String s, int left, int right) {
    int leftIncl = left - 10;
    boolean ellipseLeft = leftIncl > 0;
    if (!ellipseLeft) { leftIncl = 0; }

    int rightIncl = right + 10;
    boolean ellipseRight = s.length() > rightIncl;
    if (!ellipseRight) {
      rightIncl = s.length();
    }

    return s.substring(leftIncl, rightIncl)
            .replace("\r", "\\r")
            .replace("\n", "\\n")
            .replace("\\", "\\\\");
  }

import java.util.Locale;
  public static final void testUnopenedArray() {

  @Test
  public static final void testLongOctalNumberWithBadDigits() {
    // Found by Fabian Meumertzheim using CI Fuzz (https://www.code-intelligence.com)
    assertEquals(
            "-888888888888888888888",
            JsonSanitizer.sanitize("-0888888888888888888888")
    );
  }

  @Test
  public static final void testLongNumberInUnclosedInputWithU80() {
    // Found by Fabian Meumertzheim using CI Fuzz (https://www.code-intelligence.com)
    assertEquals(
            "{\"\":{\"\":{\"\":{\"\":{\"\":{\"\":{\"x80\":{\"\":{\"\":[-400557869725698078427]}}}}}}}}}",
            JsonSanitizer.sanitize("{{{{{{{\\x80{{([-053333333304233333333333")
    );
  }

  @Test
  public static final void testSlashFour() {
    // Found by Fabian Meumertzheim using CI Fuzz (https://www.code-intelligence.com)
    assertEquals("\"y\\u0004\"", JsonSanitizer.sanitize("y\\4")); // "y\4"
  }

  @Test
  public static final void testUnterminatedObject() {
    // Found by Fabian Meumertzheim using CI Fuzz (https://www.code-intelligence.com)
    String input = "?\u0000\u0000\u0000{{\u0000\ufffd\u0003]ve{R]\u00000\ufffd\u0016&e{\u0003]\ufffda<!.b<!<!cc1x\u0000\u00005{281<\u0000.{t\u0001\ufffd5\ufffd{5\ufffd\ufffd0\ufffd15\r\ufffd\u0000\u0000\u0000~~-0081273222428822883223759,55\ufffd\u0000\ufffd\t\u0000\ufffd";
    String got = JsonSanitizer.sanitize(input);
    String want = "{\"\":{},\"ve\":{\"R\":null},\"0\":\"e\",\"\":{},\"a<!.b<!<!cc1x\":5,\"\":{\"281\":0.0,\"\":{\"t\":5,\"\":{\"5\":0,\"15\"\r:-81273222428822883223759,\"55\"\t:null}}}}";
    assertEquals(want, got);
  }

  @Test
  public static final void testCrash1() {
    // Found by Fabian Meumertzheim using CI Fuzz (https://www.code-intelligence.com)
    String input = "?\u0000\u0000\u0000{{\u0000\ufffd\u0003]ve{R]\u00000\ufffd\ufffd\u0016&e{\u0003]\ufffda<!.b<!<!c\u00005{281<\u0000.{t\u0001\ufffd5\ufffd{515\r[\u0000\u0000\u0000~~-008127322242\ufffd\ufffd\ufffd\ufffd\ufffd\ufffd\ufffd\ufffd23759,551x\u0000\u00006{281<\u0000.{t\u0001\ufffd5\ufffd{5\ufffd\ufffd0\ufffd15\r[\u0000\u0000\u0000~~-0081273222428822883223759,\ufffd";
    String want = "{\"\":{},\"ve\":{\"R\":null},\"0\":\"e\",\"\":{},\"a<!.b<!<!c\":5,\"\":{\"281\":0.0,\"\":{\"t\":5,\"\":{\"515\"\r:[-8127322242,23759,551,6,{\"281\":0.0,\"\":{\"t\":5,\"\":{\"5\":0,\"15\"\r:[-81273222428822883223759]}}}]}}}}";
    String got = JsonSanitizer.sanitize(input);
    assertEquals(want, got);
  }

  @Test
  public static final void testDisallowedSubstrings() {
    // Found by Fabian Meumertzheim using CI Fuzz (https://www.code-intelligence.com)
    String[] inputs = {
            "x<\\script>",
            "x</\\script>",
            "x</sc\\ript>",
            "x<\\163cript>",
            "x</\\163cript>",
            "x<\\123cript>",
            "x</\\123cript>",
            "u\\u\\uu\ufffd\ufffd\\u7u\\u\\u\\u\ufffdu<\\script>5",
            "z\\<\\!--",
            "z\\<!\\--",
            "z\\<!-\\-",
            "z\\<\\!--",
            "\"\\]]\\>",
    };
    for (String input : inputs) {
      String out = JsonSanitizer.sanitize(input).toLowerCase(Locale.ROOT);
      assertFalse(out, out.contains("<!--"));
      assertFalse(out, out.contains("-->"));
      assertFalse(out, out.contains("<script"));
      assertFalse(out, out.contains("</script"));
      assertFalse(out, out.contains("]]>"));
      assertFalse(out, out.contains("<![cdata["));
    }
  }

  @Test
  public static final void testXssPayload() {
    // Found by Fabian Meumertzheim using CI Fuzz (https://www.code-intelligence.com)
    String input = "x</\\script>u\\u\\uu\ufffd\ufffd\\u7u\\u\\u\\u\ufffdu<\\script>5+alert(1)//";
    assertEquals(
            "\"x\\u003c/script>uuuu\uFFFD\uFFFDu7uuuu\uFFFDu\\u003cscript>5+alert(1)//\"",
            JsonSanitizer.sanitize(input)
    );
  }

  @Test
  public static final void testInvalidOutput() {
    // Found by Fabian Meumertzheim using CI Fuzz (https://www.code-intelligence.com)
    String input = "\u0010{'\u0000\u0000'\"\u0000\"{.\ufffd-0X29295909049550970,\n\n0";
    String want = "{\"\\u0000\\u0000\":\"\\u0000\",\"\":{\"0\":-47455995597866469744,\n\n\"0\":null}}";
    String got = JsonSanitizer.sanitize(input);
    assertEquals(want, got);
  }

  @Test
  public static final void testBadNumber() {
    String input = "¶0x.\\蹃4\\À906";
    String want = "0.0";
    String got = JsonSanitizer.sanitize(input);
    assertEquals(want, got);
  }