CVE-2026-91858
Camel-FOP: XML external entity processing - FopProducer created a TransformerFactory with only secure processing enabled, so when a third-party JAXP TransformerFactory such as Saxon-HE was on the classpath, an external DTD or entity declared in the XSL-FO input was resolved and expanded
Description
FopProducer transforms the incoming XSL-FO message body by creating a javax.xml.transform.TransformerFactory through TransformerFactory.newInstance() and enabling only FEATURE_SECURE_PROCESSING before running an identity transform over the body. On the JDK's built-in transformer, that feature alone already empties the accessExternalDTD and accessExternalStylesheet limits, so an external DTD or entity is refused. When a third-party JAXP TransformerFactory such as Saxon-HE is on the classpath, for example because the application also uses camel-xslt-saxon or camel-saxon, TransformerFactory.newInstance() returns that implementation instead, and FEATURE_SECURE_PROCESSING on its own does not restrict external resource access on it. A DOCTYPE with an external subset, or an external general entity, declared in the XSL-FO document is then resolved and expanded while the body is transformed. An external sender whose XSL-FO reaches a fop producer could therefore read files readable by the Camel process and cause the process to issue requests to hosts the document names. camel-fop does not bring such a factory itself, and excludes Xalan, so a default deployment using the JDK transformer is not affected; the issue is reachable only where another component has placed an alternative JAXP TransformerFactory on the classpath.
Mitigation
Credit
This issue was discovered by Claude Security Scan Tool
Notes
The JIRA ticket: https://issues.apache.org/jira/browse/CAMEL-24605 refers to the commits that resolved the issue, and has more details.
The fix was merged on main in https://github.com/apache/camel/pull/26108 (commit 209c67a851d3c145583d25829b7ffac0c500674b), and backported to camel-4.22.x in https://github.com/apache/camel/pull/26168 (commit f689a9c92f0e6c406f9a0256c7d940024cf56782) and to camel-4.18.x in https://github.com/apache/camel/pull/26169 (commit 9c06c6d265d70be30023e7514456b697e91db69e).
FopProducer now configures the TransformerFactory it creates with XMLConstants.ACCESS_EXTERNAL_DTD and XMLConstants.ACCESS_EXTERNAL_STYLESHEET set to the empty string, in addition to FEATURE_SECURE_PROCESSING, matching the secure XML processing configuration used by org.apache.camel.converter.jaxp.XmlConverter and elsewhere in the codebase. External DTD and external stylesheet access is therefore refused on any JAXP TransformerFactory implementation that honours those attributes, including third-party factories such as Saxon-HE whose default configuration does not restrict external access under secure processing alone. A deployment using the JDK’s built-in transformer was not affected either before or after the change, because secure processing already empties those limits on that implementation.
The issue is classified as CWE-611 (Improper Restriction of XML External Entity Reference). The camel-4.14.x line reached end of life before this fix and does not receive it; deployments on 4.14.x should move to 4.18.5 or later.