Zero Radar
← feed
CriticalVulnerabilityCVE-2026-91403updated 25 Oct 2026, 16:35 UTC

Oracle Java SE and GraalVM: remote attackers can read and change data

Java software from Oracle has a flaw in how it handles secure network connections. An attacker on the network could potentially read or change data without logging in.

Official, 2 sources
SeverityCriticalCVSS 9.1 of 10
Being exploited?UnclearNo reports either way yet
Fix available?UnclearNo fixed version published in the sources yet
How sure is this?Official, 2 sourcesBacked by an official source

How the attack works simplified

  1. 1Remote attackerSends crafted network traffic, no login needed
  2. 2Exposed web servicePasses input data to the Java APIs
  3. 3Flawed JSSE componentMishandles input in secure connection code
  4. 4Critical dataRead, changed, or deleted without authorization
  5. ResultAttacker reads or alters critical data

What happened

A flaw in the JSSE (Java Secure Socket Extension) component of Oracle Java SE, Oracle GraalVM for JDK, and Oracle GraalVM Enterprise Edition allows unauthenticated network attacks through APIs, such as web services that pass data to them.

Why it is dangerous: Successful attacks can lead to unauthorized creation, deletion, or modification of critical data, and in some cases complete access to data the product can reach. Servers and web services that process untrusted input, and client Java applets or Web Start apps running untrusted code, are at risk.

Are you affected?

You are affected if you run Oracle Java SE 8u511 (including 8u511-perf), 11.0.33, 17.0.21, 21.0.13, 25.0.5, or 27.0.1, Oracle GraalVM for JDK 17.0.21 or 21.0.13, or Oracle GraalVM Enterprise Edition 21.3.20.

Oracle Java SE: 8u511, 8u511-perf, 11.0.33, 17.0.21, 21.0.13, 25.0.5, 27.0.1; Oracle GraalVM for JDK: 17.0.21, 21.0.13; Oracle GraalVM Enterprise Edition: 21.3.20

What to do

  1. Identify all Java and GraalVM installations on your servers, clients, and build systems
  2. Check Oracle's Critical Patch Update advisory for the patched versions and apply them
  3. Until patched, restrict network access to services that pass untrusted data into Java APIs
  4. Disable or restrict Java applets and Web Start on client machines

Timeline

  1. 21 Oct 2026, 22:16 UTC
    Publicly disclosed
  2. 21 Oct 2026, 22:16 UTC
    Reported by NVD · NVD
  3. 25 Oct 2026, 16:35 UTC
    GitHub Advisory reported on it · GitHub Advisory

Sources 2 reports, oldest first

Official vendor, government CERT or advisory database

Technical details

ID
CVE-2026-91403 · GHSA-9h75-rf66-wh3r
CVSS
9.1 / 10
EPSS
0.4% chance of exploitation within 30 days
Disclosed
21 Oct 2026, 22:16 UTC
On Zero Radar
before the radar started
Last change
25 Oct 2026, 16:35 UTC

The plain-language parts and the attack diagram were written by an AI model (anthropic/claude-haiku-5.5) from the sources above. Facts like versions, exploitation and dates come from the sources themselves. How Zero Radar works

Oracle Java SE and GraalVM: remote attackers can read and change data · Zero Radar