Is CVE-2026-59903 being exploited?

No public exploit is currently tracked.

How severe is CVE-2026-59903?

CVE-2026-59903 has a CVSS v3 severity of MEDIUM (6.5).

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CVE-2026-59903

Description

Netty is an asynchronous, event-driven network application framework. Prior to 4.1.137.Final and 4.2.17.Final, io.netty.handler.codec.http.cors.CorsHandler setVaryHeader replaces application Vary headers such as Authorization or Cookie with Origin, allowing a caching proxy or CDN to reuse authenticated responses across users and disclose sensitive information. This issue is fixed in versions 4.1.137.Final and 4.2.17.Final.