CVE-2026-40682 Apache Software Foundation CVE debrief

Who should care

Users of Apache OpenNLP, especially those who use the Dictionary(InputStream) constructor to load user-supplied dictionaries, should be aware of this vulnerability. This includes developers and administrators who use OpenNLP in their applications. Immediate action is recommended to mitigate the risk of XXE attacks.

Technical summary

The DictionaryEntryPersistor class in Apache OpenNLP initializes a static SAXParserFactory at class-load time without enabling FEATURE_SECURE_PROCESSING or disabling DTD processing. When create(InputStream, EntryInserter) is invoked, the only feature set on the XMLReader is namespace support, leaving external entity resolution and DOCTYPE declarations fully enabled. This allows an attacker to supply a crafted dictionary file containing a malicious DOCTYPE declaration, triggering local file disclosure or server-side request forgery during SAX parsing.

Defensive priority

High priority should be given to upgrading to version 2.5.9 or 3.0.0-M3. In the meantime, users should ensure that all dictionary files are sourced from trusted origins and consider wrapping the Dictionary(InputStream) constructor with input validation that rejects any XML containing a DOCTYPE declaration.

Recommended defensive actions

• Upgrade to Apache OpenNLP version 2.5.9 or 3.0.0-M3.
• Ensure all dictionary files are sourced from trusted origins.
• Consider wrapping the Dictionary(InputStream) constructor with input validation that rejects any XML containing a DOCTYPE declaration.
• Monitor and restrict incoming dictionary files for suspicious or malicious content.
• Implement additional security measures, such as using a web application firewall (WAF) to detect and prevent XXE attacks.

Evidence notes

The CVE-2026-40682 vulnerability was published on May 4, 2026, and modified on June 29, 2026. The vulnerability affects Apache OpenNLP versions before 2.5.9 and before 3.0.0-M3. The CVSS score is 9.1, indicating a critical vulnerability. The vulnerability allows for XXE attacks via crafted dictionary files.

Official resources