# CVE-2026-59903: Netty: Cache Poisoning and Information Disclosure via CORS Vary Header Overwrite > Netty's CORS handler overwrites Vary headers, enabling cache poisoning and disclosure of authenticated responses to other users. - **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 17 Aug 2026 - **Updated:** 17 Aug 2026 - **Also known as:** CLEANSTART-2026-FH63085, CLEANSTART-2026-HJ08355, CLEANSTART-2026-HK72539, CLEANSTART-2026-PK10148, CLEANSTART-2026-UV29003, CLEANSTART-2026-VW00414, CLEANSTART-2026-ZN73340, DEBIAN-CVE-2026-59903, ECHO-576a-1a44-9b4d, GHSA-8c42-7qj2-3j46, MINI-2m6c-ww2c-mx56, MINI-2mf6-wrr6-64rj, MINI-37gg-24rh-p6p9, MINI-388j-rw88-r32j, MINI-3c3j-gf46-3rr9, MINI-3gm9-672w-3fp4, MINI-3h86-vm7p-8658, MINI-3m9h-jq6c-rpxj, MINI-3vrp-7hxc-3844, MINI-42j9-rcx4-2mmw, MINI-4g4f-xj24-rm97, MINI-4ghh-8phv-27g6, MINI-4pqc-4fff-7vjq, MINI-4xhg-f9r8-4mc3, MINI-533m-f29p-747c, MINI-54v7-jprv-25gc, MINI-58cm-f897-c954, MINI-5ccw-79gx-v6hr, MINI-5cr5-jjr8-gjf3, MINI-5hx6-rm9p-2mm8, MINI-5v8h-mwrj-5p6c, MINI-6g3p-qh9r-xp57, MINI-6qr2-7jqf-rxvm, MINI-6w9p-jcxx-qvpr, MINI-7242-3w27-r2wv, MINI-73j6-4h8f-mvp3, MINI-7gwx-c7xj-3jvm, MINI-7jpj-7xhv-3q4m, MINI-7pcc-qch4-5269, MINI-7qwv-cfhc-j56q, MINI-7vm8-jprp-73m7, MINI-7wrq-vf36-g468, MINI-7x9v-xhv4-h6mm, MINI-7xmf-rx2m-hcmv, MINI-88xx-849c-6wh6, MINI-8938-8wxv-jrhq, MINI-8fqp-r4qw-6vg7, MINI-8qcw-9454-jmvj, MINI-98cm-59vr-gcm4, MINI-9j82-jq86-x6cc, MINI-9p97-f4pq-qxpv, MINI-9wpj-2gmh-66v3, MINI-c4q8-m5pq-ch4q, MINI-c6gc-j6ch-w5hv, MINI-cg3x-4fqc-j2v2, MINI-chrx-7fcr-5xcx, MINI-cp57-6gvw-w559, MINI-cw6w-m5m3-jcx5, MINI-fgm7-wf8m-42gv, MINI-frhp-3wgp-jp6r, MINI-g8gf-f59c-h6vj, MINI-g9xw-6272-rf5v, MINI-gcpx-5r6q-w5hg, MINI-gcv3-8ww5-f4xp, MINI-ghxv-8393-6grr, MINI-gmm9-5fc5-cjxm, MINI-h65r-r5x4-r88v, MINI-hp26-vvgw-x6fh, MINI-j23r-9jp9-vmcf, MINI-j6fj-65mx-w6h9, MINI-jcq4-cq7h-96g7, MINI-jmj2-78xm-4v9p, MINI-m5vr-cqfq-6pw5, MINI-m8g2-745q-5648, MINI-mfv5-c94v-vc9h, MINI-mfv8-89r4-45f7, MINI-mpww-hrph-3vc3, MINI-mq5g-r9m3-xcvp, MINI-mqhm-f7cp-r355, MINI-pc67-g3v8-f6gc, MINI-phrg-gp2j-c959, MINI-q3gf-ff2m-xv5m, MINI-q62f-gw5c-hc95, MINI-q8c3-8fp3-v2q6, MINI-q8q2-f572-p275, MINI-q8xj-g588-vw2m, MINI-qjm2-h3fp-xcm8, MINI-qw42-h497-vpx9, MINI-qx2w-8432-cwmw, MINI-r44x-v8c2-ghgq, MINI-r53h-497m-qvc3, MINI-r5vj-vvmw-5665, MINI-r9f3-jvrg-33v3, MINI-r9v2-758h-q9p9, MINI-rp48-p8hr-qrr6, MINI-rv29-v4vp-5qwx, MINI-rx36-wfh7-rqch, MINI-v93q-239f-4v4p, MINI-vfp2-x4gf-mv3w, MINI-vg63-gj56-4xq6, MINI-vwm2-v984-jh3j, MINI-vxg9-9xw9-xgcp, MINI-w2r7-8ch8-w9hh, MINI-wc7m-f4p6-749g, MINI-wv69-f5xh-4q4q, MINI-wvmc-w72m-3x4q, MINI-wwrq-qrf6-w975, MINI-wxgp-7682-7r7f, MINI-x4rr-4v63-qmr3, MINI-xcv7-7pgj-5cw9, MINI-xj85-gf2c-jvv5, MINI-xpc3-37h9-8hq8, MINI-xr6h-p2mx-2qv4, UBUNTU-CVE-2026-59903 ## What is CVE-2026-59903? CVE-2026-59903 is a medium-severity vulnerability in Netty Netty, published on 17 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official 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. Weakness: CWE-524 (Use of Cache Containing Sensitive Information) ## Which versions are affected by CVE-2026-59903? 4 open source packages ship an affected version, including io.netty:netty-codec-http. It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `io.netty:netty-codec-http` | Maven | All versions | 4.1.137.Final | | `io.netty:netty-codec-http` | Maven | All versions | 4.1.137.Final | | `io.netty:netty-codec-http` | Maven | From 4.2.0.Final | 4.2.17.Final | | `io.netty:netty-codec-http` | Maven | From 4.2.0.Final | 4.2.17.Final | Products: Netty Netty. ## How do I fix CVE-2026-59903? Upgrade io.netty:netty-codec-http to a fixed version for your release line: 4.1.137.Final or 4.2.17.Final. ## Is CVE-2026-59903 being exploited? There is no known exploitation of CVE-2026-59903 in the wild and no public exploit code. Public exploit code: - CVE-2026-59903 / CVE-2026-33870: offline checker for io.netty:netty-codec-http - its 14 CVEs plus 9 advisories Netty published on 2026-09-10 that the GitHub Advisory Database (Dependabot) does not list. 4.1.137.Final / 4.2.17.Final is no longer enough; upgrade to 4.1.138.Final / 4.2.18.Final. (github_poc): https://github.com/xiaoqiMikko/netty-http-check ## Other vulnerabilities in Netty Netty - [CVE-2026-75595](https://insights.sbomify.com/CVE-2026-75595/): Netty: SNI Routing Bypass via Fragmented TLS ClientHello Causing Fallback to Default SslContext (critical 9.1) - [CVE-2026-75596](https://insights.sbomify.com/CVE-2026-75596/): Netty: Fragmented ClientHello records trigger quadratic pre-handshake reassembly in default SNI parsing (high 8.7) - [CVE-2026-59901](https://insights.sbomify.com/CVE-2026-59901/): Netty Bzip2Decoder: Infinite Loop in RLE State Machine Leads to Event-Loop Thread Hang (high 8.7) - [CVE-2026-55851](https://insights.sbomify.com/CVE-2026-55851/): Netty codec-haproxy: Signed-Byte Sentinel Collision in HAProxyMessageDecoder Leads to Unbounded Memory Exhaustion (high 8.7) - [CVE-2026-56745](https://insights.sbomify.com/CVE-2026-56745/): Netty SpdyHttpDecoder: ByteBuf Reference Leak on RST_STREAM Leads to Native Memory Exhaustion (high 8.7) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-59903 and fix it if it is affected. What it is: CVE-2026-59903 is a medium-severity vulnerability in Netty Netty, published on 17 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. Exploitation: There is no known exploitation of CVE-2026-59903 in the wild and no public exploit code. Affected packages and fixed versions: - io.netty:netty-codec-http (Maven): affected all versions; fixed in 4.1.137.Final - io.netty:netty-codec-http (Maven): affected all versions; fixed in 4.1.137.Final - io.netty:netty-codec-http (Maven): affected from 4.2.0.Final; fixed in 4.2.17.Final - io.netty:netty-codec-http (Maven): affected from 4.2.0.Final; fixed in 4.2.17.Final Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-59903/ (Markdown: https://insights.sbomify.com/CVE-2026-59903/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-59903 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-59903 - OSV: https://osv.dev/vulnerability/CVE-2026-59903 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-59903/ Summaries are generated and may contain mistakes; the official description above is the record.