Netty 4.1.136 & 4.2.16 CORSHandler Vary Header Overwrite Disclosure
CVE-2026-59903 Published on August 17, 2026
Netty: Cache Poisoning and Information Disclosure via CORS Vary Header Overwrite
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.
Vulnerability Analysis
CVE-2026-59903 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is consided to have a high level of attack complexity. The potential impact of an exploit of this vulnerability is considered to have a high impact on confidentiality, with no impact on integrity, and no impact on availability.
Weakness Type
Use of Cache Containing Sensitive Information
The code uses a cache that contains sensitive information, but the cache can be read by an actor outside of the intended control sphere. Applications may use caches to improve efficiency when communicating with remote entities or performing intensive calculations. A cache maintains a pool of objects, threads, connections, pages, financial data, passwords, or other resources to minimize the time it takes to initialize and access these resources. If the cache is accessible to unauthorized actors, attackers can read the cache and obtain this sensitive information.
Products Associated with CVE-2026-59903
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Affected Versions
netty:- Version < 4.1.137.Final is affected.
- Version >= 4.2.0.Final, < 4.2.17.Final is affected.