---
id: "CVE-2026-91484"
kind: "vulnerability"
aliases: ["CVE-2026-91484"]
title: "Java SE: plugin flaw lets low-privilege users escape the sandbox"
severity: "high"
cvss: 7.5
epss: 0.00107
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["desktop-clients", "java", "oracle-java-se", "runtime"]
not_affected_if: ["no-applets-or-web-start", "server-only-trusted-code"]
published_at: "2026-10-20T22:20:52+00:00"
first_seen_at: "2026-10-23T21:57:27+00:00"
updated_at: "2026-10-25T12:38:51+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-91484", "first_seen_at": "2026-10-23T21:57:27+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-91484", "first_seen_at": "2026-10-25T12:38:51+00:00"}]
---

# Java SE: plugin flaw lets low-privilege users escape the sandbox

The Java plugin in Oracle Java SE 8u503 has a flaw that lets an attacker with low privileges on the machine compromise the runtime. The description says the attack targets sandboxed Java Web Start applications and applets that run untrusted code from the internet.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Run `java -version` and compare against 8u503 (affected) and later builds
- Check whether Java Web Start or browser applets are enabled on client machines
- unknown for whether any server-side Java deployment is exposed

## Fix

- Upgrade Oracle Java SE 8 past `8u503` to a patched release (unknown exact fixed build)
- Disable the Java browser plugin and Java Web Start where they are not needed

## Timeline

- 2026-10-23T21:57:27+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-91484
- 2026-10-25T12:38:51+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-91484

## From the sources

Vulnerability in Oracle Java SE (component: Java plugin).  Supported versions that are affected are Oracle Java SE: 8u503 and  8u503-perf. Difficult to exploit vulnerability allows low privileged attacker with logon to the infrastructure where Oracle Java SE executes to compromise Oracle Java SE.  While the vulnerability is in Oracle Java SE, attacks may significantly impact additional products (scope change).  Successful attacks of this vulnerability can result in  unauthorized creation, deletion or modification access to critical data or all Oracle Java SE accessible data as well as  unauthorized access to critical data or complete access to all Oracle Java SE accessible data. Note: This vulnerability applies to Java deployments, typically in clients running sandboxed Java Web Start applications or sandboxed Java applets, that load and run untrusted code (e.g., code that comes from the internet) and rely on the Java sandbox for security. This vulnerability does not apply to Java deployments, typically in servers, that load and run only trusted code (e.g., code installed by an administrator). CVSS 3.1 Base Score 7.5 (Confidentiality and Integrity impacts).  CVSS Vector: (CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:N).

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