# CVE-2026-50020: Netty's HttpObjectDecoder skips arbitrary initial control characters when only initial CRLF characters are permitted > Netty's HTTP decoder improperly skips non-CRLF control characters, enabling request-boundary confusion in pipelined or multiplexed transports. - **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/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:** 12 Jun 2026 - **Updated:** 12 Jun 2026 - **Also known as:** CLEANSTART-2026-FQ42724, CLEANSTART-2026-NT22558, CLEANSTART-2026-QB68798, CLEANSTART-2026-VO96639, CLEANSTART-2026-YX18687, DEBIAN-CVE-2026-50020, ECHO-1d7b-3200-5631, GHSA-hvcg-qmg6-jm4c, MINI-29pm-3f8r-m4jh, MINI-2rjp-5c8x-chxr, MINI-32ff-2vpg-52fh, MINI-34g9-38q8-fwq5, MINI-376p-pfm9-63mr, MINI-3c34-w98q-4c22, MINI-3frq-2fv4-jpfj, MINI-3h98-846q-qrpm, MINI-3v85-845h-f25j, MINI-3x3p-w7x2-jg7r, MINI-43vp-jfm4-vc3r, MINI-4vpm-976g-2gq4, MINI-5753-g766-p348, MINI-59qh-7m5h-c5gm, MINI-5mf8-qpvj-3mp8, MINI-6643-cm4c-php8, MINI-6j7w-62p9-4qm5, MINI-6rf4-5cx8-mqj9, MINI-6wc9-xxh3-cc8j, MINI-75m9-2jx5-x55r, MINI-7fj6-crm8-f88c, MINI-7mp7-gf6w-g9cm, MINI-7p2x-pgw9-8wqp, MINI-7p5q-2rx6-v374, MINI-8g66-h5hq-gg25, MINI-8mcw-2796-vch6, MINI-8rr9-xph5-7gfq, MINI-8xqw-q526-mqqc, MINI-9358-c262-63rw, MINI-97p6-w37c-6hw2, MINI-98f9-pppr-p252, MINI-9g3p-fp5m-phh7, MINI-9qjr-f994-wwqc, MINI-9rcq-fffq-8m9q, MINI-c65h-h3f4-j222, MINI-c73x-7f4p-f528, MINI-c7c2-c824-v4hx, MINI-cvjw-5pf2-m3c9, MINI-cw86-3p26-m9hp, MINI-f5vh-2pw6-xhvf, MINI-fp43-vcwj-xx7g, MINI-fx32-6xr9-8gfw, MINI-gff6-vm8q-mp46, MINI-gqvr-26vc-c5hc, MINI-grrj-w4rm-rw8r, MINI-gwpg-r47h-2qmm, MINI-h72h-q79c-p4qf, MINI-hhmm-2vfm-587h, MINI-hmg8-xhq2-7r2m, MINI-hv64-mm2q-c683, MINI-hx4v-r2rv-5fc9, MINI-hxm2-3wq8-3875, MINI-j6qq-gv4r-67g4, MINI-jfh3-jmm8-fmwf, MINI-jg33-4292-8pp6, MINI-jg77-rv3f-fj9j, MINI-jr2g-fg2p-37vg, MINI-mch9-6c52-39w9, MINI-mm9f-x364-fgf3, MINI-p38f-vhpx-qwwv, MINI-p4qc-fmj6-q8mc, MINI-pg3c-rfjh-25r5, MINI-pgr4-prr8-ghwh, MINI-pmqq-9ccm-r37w, MINI-pr99-3j9f-7jq6, MINI-pvwh-596m-9gqc, MINI-q572-c6x6-wpjg, MINI-q948-x563-rqhx, MINI-q9wq-2v7m-jx4m, MINI-qrc2-mgq7-67hg, MINI-r4gv-rppj-5483, MINI-r655-h8w5-227x, MINI-r9qc-6q7c-r6mx, MINI-rc7m-46c7-6rgj, MINI-rhjp-32hq-9gcv, MINI-rw6q-p34w-ww68, MINI-rxpr-3fcp-8vh7, MINI-v54j-g789-9r3x, MINI-v9xg-79j5-52r3, MINI-vchq-f4m8-9wrc, MINI-vr67-q57c-pf6h, MINI-w5jj-g7q5-68v3, MINI-wr2f-phcv-wq2p, MINI-wrhg-374g-8637, MINI-wx25-v79r-42p7, MINI-wxq8-r2m9-pqq5, MINI-x7j8-jfvh-phw9, MINI-xc2g-4pjr-cv62, MINI-xgf2-hcrv-jffw, MINI-xh8p-54x6-2gwf, MINI-xmc8-9vw6-m68h, MINI-xmhr-8hh2-x7w2, ROOT-APP-MAVEN-CVE-2026-50020, UBUNTU-CVE-2026-50020 ## What is CVE-2026-50020? CVE-2026-50020 is a medium-severity vulnerability in Netty Netty, published on 12 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official description Netty is a network application framework for development of protocol servers and clients. Prior to versions 4.1.135.Final and 4.2.15.Final, before reading the first request-line, `HttpObjectDecoder` skips every byte for which `Character.isISOControl(b)` is `true` (0x00–0x1F and 0x7F) as well as all whitespace. RFC 9112 §2.2 only asks servers to ignore empty CRLF lines preceding the request-line — a carefully scoped robustness allowance intended to handle HTTP/1.0 POST workarounds. Silently absorbing NUL bytes, SOH, STX, and other non-CRLF control characters goes significantly beyond this, and can be exploited for request-boundary confusion in pipelined or multiplexed transports where a front-end component treats those bytes differently. Versions 4.1.135.Final and 4.2.15.Final patch the issue. Weakness: CWE-444 (Inconsistent Interpretation of HTTP Requests) ## Which versions are affected by CVE-2026-50020? 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 | 4.1.135.Final | | `io.netty:netty-codec-http` | Maven | All versions | 4.1.135.Final | | `io.netty:netty-codec-http` | Maven | From 4.2.0.Final | 4.2.15.Final | | `io.netty:netty-codec-http` | Maven | From 4.2.0.Final | 4.2.15.Final | Products: Netty Netty. ## How do I fix CVE-2026-50020? Upgrade io.netty:netty-codec-http to a fixed version for your release line: 4.1.135.Final or 4.2.15.Final. ## Is CVE-2026-50020 being exploited? It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-50020 exists. ## 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-2026-50020 and fix it if it is affected. What it is: CVE-2026-50020 is a medium-severity vulnerability in Netty Netty, published on 12 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-50020 exists. Affected packages and fixed versions: - io.netty:netty-codec-http (Maven): affected all versions; fixed in 4.1.135.Final - io.netty:netty-codec-http (Maven): affected all versions; fixed in 4.1.135.Final - io.netty:netty-codec-http (Maven): affected from 4.2.0.Final; fixed in 4.2.15.Final - io.netty:netty-codec-http (Maven): affected from 4.2.0.Final; fixed in 4.2.15.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-2026-50020/ (Markdown: https://insights.sbomify.com/CVE-2026-50020/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-50020 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-50020 - OSV: https://osv.dev/vulnerability/CVE-2026-50020 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-50020/ Summaries are generated and may contain mistakes; the official description above is the record.