Vulnerability Snapshot
CVE-2026-42027 is rated CRITICAL — exploitation is trivial or already observed in the wild and impact is severe. Patch immediately, not on the next maintenance window.
Affected technology: opennlp.
Executive Summary
Arbitrary Class Instantiation via Model Manifest in Apache OpenNLP ExtensionLoader
Versions Affected: before 2.5.9, before 3.0.0-M3
Description:Â
The ExtensionLoader.instantiateExtension(Class, String) method loads a class by its fully-qualified name via Class.forName() and invokes its no-arg constructor, with the class name sourced from the manifest.properties entry of a model archive. The existing isAssignableFrom check correctly rejects classes that are not subtypes of the expected extension interface (BaseToolFactory for factory=, ArtifactSerializer for serializer-class-*), but the check runs after Class.forName() has already loaded and initialized the named class.
Class.forName()Â with default initialization semantics executes the target class's static initializer before returning, so an attacker who can supply a crafted model archive can cause the static initializer of any class on the classpath to run during model loading, regardless of whether that class passes the
Why It Matters
CVE-2026-42027 is rated CRITICAL severity, requiring immediate attention from security teams.
CVSS Base Score: 9.8/10
Affected Technologies
Vendors: apache
Products: opennlp
🛡️What Defenders Should Check
Use Vulnios to continuously monitor your exposure to CVE-2026-42027 and similar vulnerabilities.
References & Sources
How Vulnios Detects This
Vulnios scans for this vulnerability using Trivy and Grype for CVE matching against your container images and OS package manifests and Nuclei templates that probe live HTTP surfaces for the published exploit pattern. Run a scan against your environment to see whether you are exposed; findings are linked back to the original CVE record so triage starts with the patch path already known.
AI Security Advisor
Powered by Gemini
Get AI-powered security recommendations tailored to this specific threat — including risk assessment, detection guidance, MITRE ATT&CK mapping, and actionable remediation steps.
Affected Products
Sources
Related Threat Alerts
- Critical Vulnerability: CVE-2026-25199 — apache — cloudstack
- Critical Vulnerability: CVE-2026-40010 — apache — wicket
- Critical Vulnerability: CVE-2016-1000031 — apache — commons_fileupload
- Critical Vulnerability: CVE-2015-1832 — apache — derby
- Critical Vulnerability: CVE-2016-5019 — apache — myfaces_trinidad
- Critical Vulnerability: CVE-2016-4436 — apache — struts
Frequently Asked Questions
What is CVE-2026-42027?
CVE-2026-42027 is a critical-severity vulnerability tracked under the Common Vulnerabilities and Exposures program. Arbitrary Class Instantiation via Model Manifest in Apache OpenNLP ExtensionLoader
Versions Affected: before 2.5.9, before 3.0.0-M3
Description:Â
The ExtensionLoader.instantiateExtension(Cl
Am I affected?
Check whether your environment runs opennlp. If you operate any of those, treat yourself as in scope until you have evidence otherwise. A Vulnios scan will identify the exact assets carrying the affected version.
How urgent is the response?
Critical: do not wait for your normal patch cycle. Verify exposure today, apply the vendor patch immediately, and add detection rules for any post-exploit indicators.
How do I remediate?
Apply the vendor patch listed in the upstream advisory linked under Sources. If the patch is not yet available, follow the vendor-supplied workaround (often a config flag or feature disable) and add detections for the published exploit pattern in your SIEM. Re-scan after the patch lands to confirm the finding clears.
Where can I track exploitation activity?
Watch CISA's Known Exploited Vulnerabilities catalog for CVE-2026-42027. Cross-reference with public exploit databases and your own SIEM/IDS for indicator-of-compromise patterns. Vulnios tracks KEV status automatically and surfaces it on the asset findings view.
How does Vulnios help with this?
Vulnios continuously cross-references your asset inventory against the live CVE feed (NVD, vendor advisories, CISA KEV, and curated OSINT). When a new CVE matches your environment, you get a prioritized finding with the severity, KEV status, exploit-prediction (EPSS), and a direct path to the vendor patch. You can start a free scan from the homepage.
Protect Your Organization
Monitor CVEs, scan for vulnerabilities, and get real-time threat alerts — all in one platform.
Get instant alerts on Telegram
Join our public channel for real-time critical CVE alerts.
Follow @vulnios