# CVE-2026-33871: Netty HTTP/2 CONTINUATION Frame Flood DoS via Zero-Byte Frame Bypass > Remote attackers can cause Denial of Service in Netty HTTP/2 servers by flooding zero-byte CONTINUATION frames, bypassing size limits and exhausting CPU resources. - **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 27 Mar 2026 - **Updated:** 15 Sep 2026 - **Also known as:** CLEANSTART-2026-EW06968, CLEANSTART-2026-FG87106, CLEANSTART-2026-RX34161, DEBIAN-CVE-2026-33871, ECHO-bdd6-9d7a-9895, GHSA-w9fj-cfpg-grvv, MINI-299j-2v79-pw6m, MINI-2cg3-8g4q-q6j7, MINI-2cm3-7w2v-r452, MINI-3f38-xmx4-hwc8, MINI-3q52-p94j-326w, MINI-3qqv-9gvx-c3rh, MINI-3w9x-pq93-hwv8, MINI-463h-fh96-f93x, MINI-4c2m-32wq-m5qx, MINI-4qc5-7333-6wj9, MINI-4r2j-v3m9-j5jx, MINI-5q4g-2cpm-cww4, MINI-5rgr-ph34-wwwh, MINI-6pv9-83gj-g68w, MINI-7274-7q7q-8qfc, MINI-7fh4-98mr-v9g9, MINI-7m52-4vfx-7qcq, MINI-7r5q-27pj-f29v, MINI-8h5m-g26p-jrj9, MINI-8jq4-rj4f-c2rx, MINI-8wr4-xv4q-pxc6, MINI-934j-749p-fj3j, MINI-978g-qjqw-7mf4, MINI-99qj-94qp-6365, MINI-9cfh-7p85-gvw3, MINI-c99h-2f6q-cqxc, MINI-cm4f-vpm5-x9g8, MINI-f5wv-3fqw-vchr, MINI-ffp9-8c2j-48jc, MINI-grjc-3cxv-p5hv, MINI-gx4j-63fc-c48w, MINI-gxpf-hgjj-86pv, MINI-hf8x-xv3r-pm3f, MINI-hgrm-8p2q-4ch8, MINI-hp32-86hj-c6mg, MINI-hxp4-qh9q-7q79, MINI-j33r-r6cc-8q8r, MINI-j5qm-fw94-4gjq, MINI-j948-6fg5-5jp5, MINI-j9p4-4f8p-34cg, MINI-j9r9-7m7m-43jj, MINI-jwh4-4643-7wq4, MINI-jx8g-g94q-5692, MINI-mq6c-vg92-4qc7, MINI-p62q-g5mm-vh2w, MINI-p756-jvw5-38rj, MINI-qcrx-2422-rjf5, MINI-qfwm-g6xh-3c4q, MINI-qqvj-8f4x-r9qv, MINI-qwj8-3mh5-8p27, MINI-rhrv-587w-856j, MINI-rmp8-fccf-ghv4, MINI-v6jg-rcfc-222x, MINI-v749-6725-j2h7, MINI-v85h-9rhw-j7g5, MINI-vcj3-c6cj-36xv, MINI-vqqj-w2xx-r6hh, MINI-wh6r-r86c-wv77, MINI-x5g4-ffx2-pgmg, MINI-x778-7r9x-mhqx, MINI-xr3w-jf6j-hvw3, MINI-xrwx-grww-65g2, MINI-xx3h-mxxm-8vmm, ROOT-APP-MAVEN-CVE-2026-33871, UBUNTU-CVE-2026-33871 ## What is CVE-2026-33871? CVE-2026-33871 is a high-severity denial of service vulnerability in Netty Netty, published on 27 Mar 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. In versions prior to 4.1.132.Final and 4.2.10.Final, a remote user can trigger a Denial of Service (DoS) against a Netty HTTP/2 server by sending a flood of `CONTINUATION` frames. The server's lack of a limit on the number of `CONTINUATION` frames, combined with a bypass of existing size-based mitigations using zero-byte frames, allows an user to cause excessive CPU consumption with minimal bandwidth, rendering the server unresponsive. Versions 4.1.132.Final and 4.2.10.Final fix the issue. Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling) ## Which versions are affected by CVE-2026-33871? 4 open source packages ship an affected version, including io.netty:netty-codec-http2. It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `io.netty:netty-codec-http2` | Maven | All versions | 4.1.132.Final | | `io.netty:netty-codec-http2` | Maven | All versions | 4.1.132.Final | | `io.netty:netty-codec-http2` | Maven | From 4.2.0.Alpha1 | 4.2.11.Final | | `io.netty:netty-codec-http2` | Maven | From 4.2.0.Alpha1 | 4.2.11.Final | Products: Netty Netty. ## How do I fix CVE-2026-33871? Upgrade io.netty:netty-codec-http2 to a fixed version for your release line: 4.1.132.Final or 4.2.11.Final. ## Is CVE-2026-33871 being exploited? There is no known exploitation of CVE-2026-33871 in the wild and no public exploit code. ## 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-2026-33871 and fix it if it is affected. What it is: CVE-2026-33871 is a high-severity denial of service vulnerability in Netty Netty, published on 27 Mar 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-2026-33871 in the wild and no public exploit code. Affected packages and fixed versions: - io.netty:netty-codec-http2 (Maven): affected all versions; fixed in 4.1.132.Final - io.netty:netty-codec-http2 (Maven): affected all versions; fixed in 4.1.132.Final - io.netty:netty-codec-http2 (Maven): affected from 4.2.0.Alpha1; fixed in 4.2.11.Final - io.netty:netty-codec-http2 (Maven): affected from 4.2.0.Alpha1; fixed in 4.2.11.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-2026-33871/ (Markdown: https://insights.sbomify.com/CVE-2026-33871/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-33871 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-33871 - OSV: https://osv.dev/vulnerability/CVE-2026-33871 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-33871/ Summaries are generated and may contain mistakes; the official description above is the record.