[SECURITY] CVE-2017-12621 Apache Commons Jelly connects to URL with custom doctype definitions.

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[SECURITY] CVE-2017-12621 Apache Commons Jelly connects to URL with custom doctype definitions.

Rob Tompkins-2
CVE-2017-12621: Apache Commons Jelly connects to URL with custom doctype definitions.

Severity: Medium

Vendor:
The Apache Software Foundation

Versions Affected:
commons-jelly-1.0 (core), namely commons-jelly-1.0.jar

Description:
During Jelly (xml) file parsing with Apache Xerces, if a custom doctype entity is declared with a “SYSTEM” entity with a URL and that entity is used in the body of the Jelly file, during parser instantiation the parser will attempt to connect to said URL. This could lead to XML External Entity (XXE) attacks. The Open Web Application Security Project suggests that the fix be https://www.owasp.org/index.php/XML_External_Entity_(XXE)_Prevention_Cheat_Sheet#XMLReader

Mitigation:
1.0 users should migrate to 1.0.1.

Example:

example.jelly
--------------
<?xml version="1.0"?>
<!---
 Licensed to the Apache Software Foundation (ASF) under one or more
 contributor license agreements.  See the NOTICE file distributed with
 this work for additional information regarding copyright ownership.
 The ASF licenses this file to You under the Apache License, Version 2.0
 (the "License"); you may not use this file except in compliance with
 the License.  You may obtain a copy of the License at
      http://www.apache.org/licenses/LICENSE-2.0
 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
-->
<!DOCTYPE r [
        <!ELEMENT r ANY >
        <!ENTITY sp SYSTEM "http://127.0.0.1:4444/">
        ]>
<r>&sp;</r>
<j:jelly trim="false" xmlns:j="jelly:core"
         xmlns:x="jelly:xml"
         xmlns:html="jelly:html">
</j:jelly>
--------------

ExampleParser.java
------------------
public class ExampleParser {
       
        public static void main(String[] args) throws JellyException, IOException,
                                        NoSuchMethodException, IllegalAccessException,IllegalArgumentException,
                                        InvocationTargetException {
                JellyContext context = new JellyContext();
                context.runScript("example.jelly", null);
        }
}

Credit:
This was discovered by Luca Carettoni of Doyensec.

References:
[1] http://commons.apache.org/jelly/security-reports.html
[2] https://issues.apache.org/jira/browse/JELLY-293


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