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XmlUtil의 XML 외부 엔티티(XXE) 취약점 수정 #138

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XmlUtil의 XML 외부 엔티티(XXE) 취약점 수정 #138

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33 changes: 33 additions & 0 deletions egovframework.dev.imp.core/src/egovframework/dev/imp/core/utils/XmlUtil.java
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@
import java.io.StringReader;
import java.io.StringWriter;

import javax.xml.XMLConstants;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
Expand All @@ -47,6 +48,35 @@ public class XmlUtil {
static {
factory.setValidating(false);
vfactory.setValidating(true);
// XXE(XML External Entity) 취약점 방지
applyXxeProtection(factory, false);
applyXxeProtection(vfactory, true);
}

/**
* XXE(XML External Entity Injection, CWE-611) 취약점을 방지하기 위해
* 외부 엔티티 처리를 제한한다.
*
* 외부 일반/파라미터 엔티티를 차단하면 검증 여부와 무관하게 외부 엔티티를 통한
* 로컬 파일 읽기·SSRF를 막을 수 있다. 스키마 검증(validating=true)이 필요한
* 파서는 DTD 로딩을 유지해야 하므로 외부 엔티티 차단만 적용한다.
*
* @param dbf 보호를 적용할 DocumentBuilderFactory
* @param validating 검증 파서 여부(true면 DTD 로딩을 유지)
*/
private static void applyXxeProtection(DocumentBuilderFactory dbf, boolean validating) {
try {
dbf.setFeature("http://xml.org/sax/features/external-general-entities", false);
dbf.setFeature("http://xml.org/sax/features/external-parameter-entities", false);
dbf.setXIncludeAware(false);
dbf.setExpandEntityReferences(false);
if (!validating) {
dbf.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", false);
dbf.setFeature(XMLConstants.FEATURE_SECURE_PROCESSING, true);
}
} catch (ParserConfigurationException e) {
// 특정 기능을 지원하지 않는 파서에서도 나머지 방어는 적용되도록 무시한다.
}
}

public static Node getRootNode(String filePath) throws Exception{
Expand Down Expand Up @@ -184,6 +214,7 @@ public static void addNode(Node contextNode, String xPath, String xmlStr) throws
Node parentsNode = componentList.item(0);

DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
applyXxeProtection(factory, false);
DocumentBuilder builder = factory.newDocumentBuilder();
Document doc = builder.parse(new InputSource(new StringReader(xmlStr)));
Node node = doc.getDocumentElement();
Expand All @@ -202,6 +233,7 @@ public static void addNode(Node contextNode, String xPath, String xmlStr, String
Node parentsNode = componentList.item(0);

DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
applyXxeProtection(factory, false);
DocumentBuilder builder = factory.newDocumentBuilder();
Document doc = builder.parse(new InputSource(new StringReader(xmlStr)));
Node node = doc.getDocumentElement();
Expand All @@ -225,6 +257,7 @@ public static void addFirstNode(Node contextNode, String xPath, String xmlStr, S
Node parentsNode = componentList.item(0);

DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
applyXxeProtection(factory, false);
DocumentBuilder builder = factory.newDocumentBuilder();
Document doc = builder.parse(new InputSource(new StringReader(xmlStr)));
Node node = doc.getDocumentElement();
Expand Down
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