Vulnerability in io.netty:netty-codec-http (CVE-2026-59903)
Summary
Vulnerability in io.netty:netty-codec-http (CVE-2026-59903). Confidential information can be exposed externally. Exploitable via CorsHandler. Mitigation: upgrade to 4.1.137.Final or later.
Original description
The description as published by the source.
Summary
Netty's CorsHandler silently overwrites existing Vary headers, enabling cache poisoning and sensitive information disclosure.
Details
io.netty.handler.codec.http.cors.CorsHandler#setVaryHeader overwrites any existing Vary headers set by backend applications.
private static void setVaryHeader(final HttpResponse response) {
response.headers().set(HttpHeaderNames.VARY, HttpHeaderNames.ORIGIN);
}
Because set() replaces all existing values for the header, if a backend application sets a Vary header (such as Vary: Authorization or Vary: Cookie) to ensure that intermediate caches (like CDNs) cache responses separately per user, the CorsHandler will overwrite it with Vary: origin. This causes the caching proxy to ignore the authorization context and cache the response based solely on the URL and Origin, allowing an attacker to retrieve another user's cached sensitive data.
Impact
This is a Cache Poisoning vulnerability that leads to Information Disclosure. It impacts any Netty-based web application that uses the CorsHandler, sets its own Vary headers to manage caching of authenticated or user-specific responses (e.g., Vary: Authorization), and is deployed behind a caching proxy or CDN. The end-users of these applications are impacted, as their sensitive data may be leaked to unauthorized actors.
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-59903 has been found in io.netty:netty-codec-http.
Attackers can target a specific entry point like CorsHandler over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 6.5/10.
What to do: upgrade io.netty:netty-codec-http to 4.1.137.Final or later.
If unsure, ask your IT team or search "io.netty:netty-codec-http CVE-2026-59903" on the vendor's site.
CVE-2026-59903 (io.netty:netty-codec-http) — CWE-524 / CVSS v3 6.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: CorsHandler / Vary
Patched: 4.1.137.Final — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-524) exists in io.netty:netty-codec-http. Attackers reach the vulnerable code path via CorsHandler without authentication.
Check the vendor advisory for the affected versions of io.netty:netty-codec-http. Attack surface: CorsHandler / Vary.
Severity: Medium (CVSS 6.5/10). Confidential information can be exposed externally.
Update to 4.1.137.Final.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Audit SBOM/dependencies to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
Audit SBOM/dependencies for affected components.資産台帳・SBOM・依存マニフェストで io.netty:netty-codec-http を使っているサービスとバージョンを洗い出す。
-
2Apply patch patch
Upgrade io.netty:netty-codec-http to 4.1.137.Finalステージング環境で 4.1.137.Final に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2026-59903 netty
- Ubuntu UBUNTU-CVE-2026-59903 netty