CVE-2026-42027: Arbitrary Class Instantiation via Model Manifest in Apache OpenNLP ExtensionLoader Versions Affected: bef

Q: How do I fix CVE-2026-42027?

opennlp: upgrade to 2.5.9. Exact commands for each OS are on this page.

Q: Is CVE-2026-42027 being exploited?

CVE-2026-42027 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-42027 affect?

CVE-2026-42027 affects opennlp. Severity is critical (CVSS 9.8). Arbitrary Class Instantiation via Model Manifest in Apache OpenNLP ExtensionLoader Versions Affected: before 1.9.5, before 2.5.9, before 3.0.0-M3 Description: The ExtensionLoader.instantiateExtension(Class, String) method loads

Q: How urgent is CVE-2026-42027?

Priority 61/100. Critical severity; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action; On your watchlist

This week

CRITICAL 9.8REMOTEWATCHLISTUPGRADE

CVE-2026-42027 is a critical-severity flaw (CVSS 9.8) affecting opennlp. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Arbitrary Class Instantiation via Model Manifest in Apache OpenNLP ExtensionLoader Versions Affected: before 1.9.5, before 2.5.9, before 3.0.0-M3 Description: 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

Why this priority

Critical severity
CISA SSVC: automatable with total technical impact
Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.7% (top 47%)
CISA exploited list	No
Weakness	CWE-470, CWE-502
Published	2026-05-04
Last modified	2026-10-26

Publisher (CNA): Apache Software Foundation · Vendor: apache

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-05-04 17:16 UTCPublished CVE record published
2026-10-26 19:10 UTCUpdated Record last modified

apache opennlp UPGRADE

Affected: < 2.5.9 · 3.0.0 m1 · 3.0.0 m2

Fixed in: 2.5.9

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy opennlp || rpm -q opennlp || opennlp --version

2. UPGRADE to 2.5.9 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade opennlp

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade opennlp

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Exact fixes by distribution

Maven · org.apache.opennlp:opennlp-tools · FIXED · 3.0.0-M3 · vulnerable: >= 3.0.0-M1, < 3.0.0-M3 · source

Set org.apache.opennlp:opennlp-tools to 3.0.0-M3 or later in pom.xml or build.gradle, then rebuild and redeploy.

Fedora 46 · ddnet · FIXED · 20.2-1.fc46 · FEDORA-2026-6991b4ab14 · source

sudo dnf upgrade --advisory=FEDORA-2026-6991b4ab14

Fedora ELN · libplacebo · FIXED · 7.360.1-5.eln159 · FEDORA-2026-92226f221e · source

sudo dnf upgrade --advisory=FEDORA-2026-92226f221e

Debian 12 · apache-opennlp · NO FIX YET

Debian 13 · apache-opennlp · NO FIX YET

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-42027?

opennlp: upgrade to 2.5.9. Exact commands for each OS are on this page.

Is CVE-2026-42027 being exploited?

CVE-2026-42027 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-42027 affect?

CVE-2026-42027 affects opennlp. Severity is critical (CVSS 9.8). Arbitrary Class Instantiation via Model Manifest in Apache OpenNLP ExtensionLoader Versions Affected: before 1.9.5, before 2.5.9, before 3.0.0-M3 Description: The ExtensionLoader.instantiateExtension(Class, String) method loads

How urgent is CVE-2026-42027?

Priority 61/100. Critical severity; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action; On your watchlist

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CVE-2026-43825 HIGH 7.3 DOWNGRADE Untrusted Java Deserialization in Apache OpenNLP SvmDoccatModel Versions Affected: before 3.0.0-M4 (libsvm
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CVE-2026-82617 CRITICAL 9.8 UPGRADE The two built-in name-finder patterns exposed by opennlp.tools.namefind.RegexNameFinderFactory - DEFAULT_REGEX

References

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