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fix(java): treat ACCESS_EXTERNAL_DTD as an XXE sanitizer #4024

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fix(java): treat ACCESS_EXTERNAL_DTD as an XXE sanitizer #4024

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ec86e96
fix(java): treat ACCESS_EXTERNAL_DTD="" as an XXE sanitizer
Eljees Jul 28, 2026
102f6ec
fix(java): match only the JAXP ACCESS_EXTERNAL_DTD symbol
Eljees Jul 28, 2026
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12 changes: 12 additions & 0 deletions java/lang/security/audit/xxe/documentbuilderfactory-disallow-doctype-decl-missing.fixed.java
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.XMLConstants;


class GoodDocumentBuilderFactory {
Expand Down Expand Up @@ -167,3 +168,14 @@ private void setFeatures(DocumentBuilderFactory dbf) throws Exception {
}

}

class GoodDocumentBuilderFactoryAccessExternalDtd {
public void blockExternalDtd() throws ParserConfigurationException {
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
dbf.setFeature(XMLConstants.FEATURE_SECURE_PROCESSING, true);
dbf.setAttribute(XMLConstants.ACCESS_EXTERNAL_DTD, "");
dbf.setAttribute(XMLConstants.ACCESS_EXTERNAL_SCHEMA, "");
//ok:documentbuilderfactory-disallow-doctype-decl-missing
dbf.newDocumentBuilder();
}
}
12 changes: 12 additions & 0 deletions java/lang/security/audit/xxe/documentbuilderfactory-disallow-doctype-decl-missing.java
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.XMLConstants;


class GoodDocumentBuilderFactory {
Expand Down Expand Up @@ -163,3 +164,14 @@ private void setFeatures(DocumentBuilderFactory dbf) throws Exception {
}

}

class GoodDocumentBuilderFactoryAccessExternalDtd {
public void blockExternalDtd() throws ParserConfigurationException {
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
dbf.setFeature(XMLConstants.FEATURE_SECURE_PROCESSING, true);
dbf.setAttribute(XMLConstants.ACCESS_EXTERNAL_DTD, "");
dbf.setAttribute(XMLConstants.ACCESS_EXTERNAL_SCHEMA, "");
//ok:documentbuilderfactory-disallow-doctype-decl-missing
dbf.newDocumentBuilder();
}
}
5 changes: 5 additions & 0 deletions java/lang/security/audit/xxe/documentbuilderfactory-disallow-doctype-decl-missing.yaml
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Expand Up @@ -113,6 +113,11 @@ rules:
...

$FACTORY.setFeature("http://xml.org/sax/features/external-general-entities", false);
- patterns:
- pattern: $FACTORY.setAttribute($ATTR, "")
- metavariable-regex:
metavariable: $ATTR
regex: ^(.*\.)?ACCESS_EXTERNAL_DTD$

@chatgpt-codex-connector chatgpt-codex-connector Bot Jul 28, 2026

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P1 Badge Restrict the sanitizer to the JAXP XMLConstants symbol

When application code has any other expression ending in ACCESS_EXTERNAL_DTD, this regex suppresses the XXE finding without checking what property that expression represents. For example, a local String ACCESS_EXTERNAL_DTD = XMLConstants.ACCESS_EXTERNAL_SCHEMA; followed by dbf.setAttribute(ACCESS_EXTERNAL_DTD, "") matches this sanitizer even though external DTD/entity access remains enabled. Match XMLConstants.ACCESS_EXTERNAL_DTD explicitly, and handle the statically imported form only when the corresponding javax.xml.XMLConstants static import is present.

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@chatgpt-codex-connector chatgpt-codex-connector Bot Jul 28, 2026

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P2 Badge Recognize the property in static initializers

When a static factory field is hardened in a static initializer and consumed from another method, this sanitizer is in a different taint scope from newDocumentBuilder() and does not prevent the field-use source from firing. The source section explicitly has pattern-not-inside exceptions for the existing setFeature mitigations but no equivalent for setAttribute(XMLConstants.ACCESS_EXTERNAL_DTD, ""), so the new mitigation still produces a false positive in that established static-field pattern.

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@chatgpt-codex-connector chatgpt-codex-connector Bot Jul 28, 2026

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P2 Badge Recognize the property when applied by a helper

When callers pass the factory to a local hardening helper that sets ACCESS_EXTERNAL_DTD, this direct-call sanitizer does not match the helper invocation, so the later newDocumentBuilder() remains reported. The rule already has a separate helper-method sanitizer branch for each accepted setFeature defense, but this change does not add the new setAttribute defense there; the same abstraction demonstrated by GoodDocumentBuilderFactoryCtr2 therefore stops working for the newly supported mitigation.

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@chatgpt-codex-connector chatgpt-codex-connector Bot Jul 28, 2026

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P1 Badge Re-taint factories when external DTD access is restored

When code first sets ACCESS_EXTERNAL_DTD to "" but later changes the same property to a permissive value such as "all" before constructing the builder, this by-side-effect sanitizer permanently clears the factory's taint and the sink is missed even though external entity resolution is enabled again. The analogous insecure setFeature(..., true/false) mutations have dedicated rules, but there is no rule or taint source for a nonempty ACCESS_EXTERNAL_DTD assignment, so this change introduces an uncovered XXE false negative unless such assignments re-taint the factory.

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- focus-metavariable: $FACTORY
- patterns:
- pattern-either:
Expand Down