Affects widely used Oracle Java SE and GraalVM runtimes; remote unauthenticated network exploit with full data compromise potential; high CVSS (9.1).
CVE-2026-91403
Remote unauthenticated JSSE flaw in Oracle Java/GraalVM enabling full data compromise
Is CVE-2026-91403 being exploited?
Not confirmed. CVE-2026-91403 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.31% probability of exploitation in the next 30 days.
How severe is CVE-2026-91403?
CVE-2026-91403 is rated Critical with a CVSS score of 9.1. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-91403?
Yes. A fix has been recorded for CVE-2026-91403. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-91403 affect?
CVE-2026-91403 affects Oracle Java SE 8u511, Oracle Java SE 8u511-perf, Oracle Java SE 11.0.33, Oracle Java SE 17.0.21, and 6 further products or versions. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-91403?
Apply Oracle security update immediately; isolate/block vulnerable Java services until patched.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote, unauthenticated network exploit via JSSE APIs allows unauthorized creation, deletion, modification or full access to Java/GraalVM accessible data.
Immediate action required
- affected21.3.20
- affected17.0.21
- affected21.0.13
- affected8u511
- affected8u511-perf
- affected11.0.33
- affected17.0.21
- affected21.0.13
- affected25.0.5
- affected27.0.1
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.