Is CVE-2026-91403 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-91403 being exploited in the wild.

How severe is CVE-2026-91403?

Critical severity, with a CVSS score of 9.1, published 21 October 2026.

Which products and versions are affected?

Oracle GraalVM Enterprise Edition 21.3.20; Oracle Graalvm For Jdk 17.0.21, 21.0.13; Oracle Java SE 8u511, 8u511-perf, 11.0.33, 17.0.21, 21.0.13, 25.0.5, 27.0.1.

Is there a fix for CVE-2026-91403?

No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

How is CVE-2026-91403 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-91403?

Check whether you run Oracle GraalVM Enterprise Edition, Oracle Graalvm For Jdk or Oracle Java SE at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-91403: Oracle Java SE JSSE remote data exposure and modification

CVE-2026-91403 · Severity: critical · CVSS 9.1 · Published 2026-10-21

A critical vulnerability in the Java Secure Socket Extension (JSSE) component of Oracle Java SE and GraalVM allows remote attackers to read, modify, or delete sensitive data without authentication. An attacker can exploit this through network-based protocols or by supplying malicious data to Java applications, including web services and Java Web Start applets, potentially exposing or corrupting all accessible information.

Technologies: Oracle GraalVM Enterprise Edition, Oracle Graalvm For Jdk, Oracle Java SE. Vendors: Oracle.

Quick answers

Is CVE-2026-91403 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-91403 being exploited in the wild.
How severe is CVE-2026-91403?: Critical severity, with a CVSS score of 9.1, published 21 October 2026.
Which products and versions are affected?: Oracle GraalVM Enterprise Edition 21.3.20; Oracle Graalvm For Jdk 17.0.21, 21.0.13; Oracle Java SE 8u511, 8u511-perf, 11.0.33, 17.0.21, 21.0.13, 25.0.5, 27.0.1.
Is there a fix for CVE-2026-91403?: No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-91403 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-91403?: Check whether you run Oracle GraalVM Enterprise Edition, Oracle Graalvm For Jdk or Oracle Java SE at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

A remote code execution or data corruption vulnerability exists in the JSSE (Java Secure Socket Extension) component, exploitable without authentication over network protocols. The vulnerability affects multiple Java SE versions and GraalVM distributions; attackers can gain unauthorized read, write, and delete access to critical data by sending specially crafted data to affected APIs or web services. No authentication or user interaction is required for exploitation.

Affected products

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

Timeline

2026-10-21: disclosed

References

https://www.oracle.com/security-alerts/alert-cve-2026-91403.html

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