# CVE-2026-59921: Netty: CRLF Injection via Multipart Filename in Netty HttpPostRequestEncoder > Attackers can inject arbitrary MIME headers into multipart requests via unsanitized filenames, potentially bypassing security controls or corrupting data. - **Severity:** Medium 5.7 (`CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N`) - **Exploited in the wild:** Not known - **Login needed:** Any signed-in user - **Attackable:** Local or same network only - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 28 Jul 2026 - **Updated:** 29 Jul 2026 - **Also known as:** CLEANSTART-2026-AC10383, CLEANSTART-2026-BL92558, CLEANSTART-2026-CK01312, CLEANSTART-2026-CP85393, CLEANSTART-2026-SM87861, DEBIAN-CVE-2026-59921, ECHO-0fed-b326-7314, GHSA-gcjf-9mgh-3p7g, MINI-228g-q4r3-46vw, MINI-26g6-93c7-cr9g, MINI-27r9-fgpg-gm82, MINI-2f83-jqqr-4wrm, MINI-2fhh-6wq7-5376, MINI-2ph4-mppp-j44w, MINI-2prc-hc97-292r, MINI-2xjx-3mm8-4w8m, MINI-33gh-4g27-p3mp, MINI-3fmw-vj93-h2gc, MINI-3m6w-vfg7-8rx3, MINI-3r25-p9pw-825q, MINI-47wm-xr4c-8393, MINI-4f3r-5mc8-hj94, MINI-56jf-69xx-99pf, MINI-5mxj-vfvj-ch5w, MINI-5rpr-596c-q44h, MINI-5vcp-qv66-wh4x, MINI-62f2-fr8v-6gpx, MINI-643h-j95w-7xfx, MINI-6627-9v73-34j4, MINI-6qvx-7ff4-f9w7, MINI-6w5m-jgr2-w4fq, MINI-75gr-jf8v-22xj, MINI-76pj-h28q-55r2, MINI-7jf3-4x2v-hg8f, MINI-7wcj-gr65-6mpq, MINI-7x56-3cgx-c3j3, MINI-849c-f9v9-p4jv, MINI-88q4-fgm7-jg3r, MINI-8f9x-wqp7-m76q, MINI-8jwv-rp28-j7qg, MINI-8rc9-fh65-w7h9, MINI-8w89-gx7g-r2wq, MINI-8x4j-g759-8733, MINI-95fx-gx3p-574g, MINI-9qcj-w975-g8cj, MINI-9rxf-m4g6-jfxj, MINI-c2j6-p2c9-cwf7, MINI-c477-p8fw-jr7v, MINI-c5ff-r82r-369g, MINI-c77m-h3h3-v9jq, MINI-ccr7-ch8r-5p92, MINI-chvm-x6px-pvx2, MINI-cjj8-x3hq-xvhj, MINI-cjpw-xf32-xwvm, MINI-f45x-2m43-rg2v, MINI-fx52-wjx7-jrvh, MINI-gm2r-fpfc-f93g, MINI-gw63-3wcr-x34w, MINI-gw6m-5jrj-w6pv, MINI-hg44-prm7-w3q4, MINI-hggx-ccj7-5c5x, MINI-hgmv-pfv4-vw8j, MINI-hmhr-xxw6-94wf, MINI-hqr9-wr25-rm49, MINI-jcgq-gf78-pq6v, MINI-jcww-pgrv-6xw5, MINI-jg3v-fjx9-659x, MINI-jj2h-9wcc-wwf6, MINI-jmhv-7f58-xm79, MINI-jrm2-j6p2-x6qq, MINI-jx55-jpf6-35xv, MINI-m4qf-2m3x-649v, MINI-m4rc-vxcx-xv24, MINI-m9xv-3vp5-4797, MINI-mhpw-x4wf-8r55, MINI-mvf5-mw2m-885g, MINI-mvgg-mjpc-gcx9, MINI-mwxx-4f5w-hj7q, MINI-p43r-hcmr-5wwg, MINI-p52g-7673-42c8, MINI-p5rf-3p29-r8h4, MINI-p9hj-wfm6-54r8, MINI-phpq-7x5h-r3p2, MINI-q4p6-6cp6-4xpx, MINI-q9m4-j28p-7v3f, MINI-qhc8-489x-q5mf, MINI-qhhf-gqc5-5qx3, MINI-qp48-957v-69gw, MINI-r47r-79r6-3578, MINI-r6c6-2q4p-2728, MINI-r9q3-329c-qfg7, MINI-rg99-7q9p-pvv6, MINI-rhh5-hrhr-h56f, MINI-rx5f-h72w-pq8r, MINI-v7hx-45hx-xfh5, MINI-vgc7-5mg3-7jvm, MINI-vgmj-fmw2-xcw7, MINI-vp8f-5ww3-xcgj, MINI-vpcv-9jm2-8mr8, MINI-vx2g-5fgc-8996, MINI-w38v-85hc-5f9h, MINI-w87x-fg28-79xp, MINI-wfff-q889-vhc5, MINI-wgg8-3fcc-x2h4, MINI-wphp-hq35-2f4q, MINI-wwww-gx4p-qw68, MINI-wx6j-74qv-wrq8, MINI-x77x-f252-wgff, MINI-x973-86vh-w5rr, MINI-xcg8-p97v-rj4f, MINI-xf57-f8j8-24g9, MINI-xppf-p4cw-qfqm, MINI-xqhv-f228-fx42, UBUNTU-CVE-2026-59921 ## What is CVE-2026-59921? CVE-2026-59921 is a medium-severity vulnerability in Netty Netty, published on 28 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim. ### Official description Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.136.Final and 4.2.16.Final, HttpPostRequestEncoder constructs multipart HTTP request bodies by directly concatenating user-supplied filenames and field names into Content-Disposition MIME headers without validating or sanitizing CRLF characters (\r\n). Since MIME headers are delimited by CRLF, an attacker who controls the filename can inject arbitrary MIME headers into the multipart body part. The root cause is that neither the encoder nor the FileUpload implementations' setFilename() methods, which only check for null, neutralize CRLF characters before the filename is embedded into the header. This issue has been fixed in versions 4.1.136.Final and 4.2.16.Final. Weakness: CWE-93 (Improper Neutralization of CRLF Sequences) ## Which versions are affected by CVE-2026-59921? 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 | 4.1.136.Final | | `io.netty:netty-codec-http` | Maven | All versions | 4.1.136.Final | | `io.netty:netty-codec-http` | Maven | From 4.2.0.Final | 4.2.16.Final | | `io.netty:netty-codec-http` | Maven | From 4.2.0.Final | 4.2.16.Final | Products: Netty Netty. ## How do I fix CVE-2026-59921? Upgrade io.netty:netty-codec-http to a fixed version for your release line: 4.1.136.Final or 4.2.16.Final. ## Is CVE-2026-59921 being exploited? It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-59921 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-2026-59921 and fix it if it is affected. What it is: CVE-2026-59921 is a medium-severity vulnerability in Netty Netty, published on 28 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim. Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-59921 exists. Affected packages and fixed versions: - io.netty:netty-codec-http (Maven): affected all versions; fixed in 4.1.136.Final - io.netty:netty-codec-http (Maven): affected all versions; fixed in 4.1.136.Final - io.netty:netty-codec-http (Maven): affected from 4.2.0.Final; fixed in 4.2.16.Final - io.netty:netty-codec-http (Maven): affected from 4.2.0.Final; fixed in 4.2.16.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-2026-59921/ (Markdown: https://insights.sbomify.com/CVE-2026-59921/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-59921 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-59921 - OSV: https://osv.dev/vulnerability/CVE-2026-59921 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-59921/ Summaries are generated and may contain mistakes; the official description above is the record.