Io.netty:netty codec http: Netty Vulnerable to Cache Poisoning and Information Disclosure via CORS Vary Header Overwrite (CVE-2026-59903)
Netty's CorsHandler component overwrites existing Vary headers with a fixed 'Vary: origin' header, ignoring any previously set Vary headers such as 'Vary: Authorization' or 'Vary: Cookie'. This behavior can cause caching proxies or CDNs to cache authenticated or user-specific responses incorrectly, leading to cache poisoning and potential sensitive information disclosure to unauthorized users.
AI Analysis
Technical Summary
The vulnerability in io.netty.handler.codec.http.cors.CorsHandler arises because its setVaryHeader method replaces any existing Vary headers with 'Vary: origin'. Backend applications that rely on setting Vary headers like 'Authorization' or 'Cookie' to control caching per user are affected because the CorsHandler silently overwrites these headers. When deployed behind caching proxies or CDNs, this can cause cached responses to be served to unauthorized users, resulting in information disclosure. This issue is tracked as CVE-2026-59903 with a CVSS 3.1 base score of 6.5 (medium severity).
Potential Impact
Applications using Netty's CorsHandler that set their own Vary headers to manage user-specific caching and are deployed behind caching proxies or CDNs risk cache poisoning. This can lead to unauthorized disclosure of sensitive user data cached and served incorrectly due to the overwritten Vary header. The confidentiality of user data is impacted, while integrity and availability are not significantly affected.
Mitigation Recommendations
A patch is available to address this vulnerability. Users of Netty's CorsHandler should apply the official fix provided by the vendor to ensure that existing Vary headers are preserved rather than overwritten. Until patched, avoid relying solely on CorsHandler for CORS handling if your application sets user-specific Vary headers and is deployed behind caching proxies or CDNs.
Io.netty:netty codec http: Netty Vulnerable to Cache Poisoning and Information Disclosure via CORS Vary Header Overwrite (CVE-2026-59903)
Description
Netty's CorsHandler component overwrites existing Vary headers with a fixed 'Vary: origin' header, ignoring any previously set Vary headers such as 'Vary: Authorization' or 'Vary: Cookie'. This behavior can cause caching proxies or CDNs to cache authenticated or user-specific responses incorrectly, leading to cache poisoning and potential sensitive information disclosure to unauthorized users.
CVSS v3.1
Score 6.5medium
Affected software
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The vulnerability in io.netty.handler.codec.http.cors.CorsHandler arises because its setVaryHeader method replaces any existing Vary headers with 'Vary: origin'. Backend applications that rely on setting Vary headers like 'Authorization' or 'Cookie' to control caching per user are affected because the CorsHandler silently overwrites these headers. When deployed behind caching proxies or CDNs, this can cause cached responses to be served to unauthorized users, resulting in information disclosure. This issue is tracked as CVE-2026-59903 with a CVSS 3.1 base score of 6.5 (medium severity).
Potential Impact
Applications using Netty's CorsHandler that set their own Vary headers to manage user-specific caching and are deployed behind caching proxies or CDNs risk cache poisoning. This can lead to unauthorized disclosure of sensitive user data cached and served incorrectly due to the overwritten Vary header. The confidentiality of user data is impacted, while integrity and availability are not significantly affected.
Mitigation Recommendations
A patch is available to address this vulnerability. Users of Netty's CorsHandler should apply the official fix provided by the vendor to ensure that existing Vary headers are preserved rather than overwritten. Until patched, avoid relying solely on CorsHandler for CORS handling if your application sets user-specific Vary headers and is deployed behind caching proxies or CDNs.
Technical Details
- Gcve Source
- db.gcve.eu
- Osv Id
- GHSA-8c42-7qj2-3j46
- Osv Schema Version
- 1.4.0
- Aliases
- ["CVE-2026-59903"]
- Ecosystems
- ["Maven"]
- Database Specific Severity
- MODERATE
- Cvss Version
- 3.1
Threat ID: 6a838c4cbf8831d539b4ca63
Added to database: 08/17/2026, 22:33:48 UTC
Last enriched: 08/20/2026, 03:28:23 UTC
Last updated: 10/02/2026, 02:46:05 UTC
Views: 50
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