# CVE-2026-56819: Netty: HTTP/2 decompression leaks ByteBuf reference count when the decompressor channel is already closed (Direct memory leak / OOM DoS) > Remote attackers can cause a denial of service by exhausting direct memory in Netty applications using HTTP/2 decompression. - **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 21 Jul 2026 - **Updated:** 23 Jul 2026 - **Also known as:** CLEANSTART-2026-CP47219, CLEANSTART-2026-DG55776, CLEANSTART-2026-PW77376, CLEANSTART-2026-TY09465, DEBIAN-CVE-2026-56819, ECHO-7258-9374-4a42, GHSA-93wv-jw9v-4972, MINI-27h3-p4qw-h4gh, MINI-2c43-742m-h97j, MINI-2gp5-jhrg-f6p6, MINI-2jvv-jwrj-6wv4, MINI-2r4q-x97q-jp6r, MINI-339c-5vr4-rj6w, MINI-3fr7-vcmw-vhp6, MINI-3q8j-g2wc-qpgp, MINI-3wmx-qc5r-m7cv, MINI-44pv-2m65-c8gx, MINI-489r-r39g-ghjq, MINI-4gpv-r4ph-rrpp, MINI-524f-5hv3-chfg, MINI-5r55-wm7p-7jhc, MINI-62wq-cmhj-r95r, MINI-63cf-2rpw-vc6r, MINI-63xg-jfvc-r589, MINI-683r-pfj7-w47g, MINI-6f2w-7m8x-5wv5, MINI-6ggm-62h2-hjg3, MINI-6qr5-9g6v-vp56, MINI-72x7-qppw-jvjx, MINI-77m5-6m78-f8fx, MINI-77vw-8wvw-cv8m, MINI-78p7-qqhh-7q6x, MINI-7cpc-mw56-wp83, MINI-7f4h-7rxx-6hq6, MINI-7mjj-wp4g-5p5q, MINI-8pxp-m6hr-qj68, MINI-8x95-fhfc-5mqw, MINI-92rw-4qxq-q2j6, MINI-95xw-7hv5-9v7c, MINI-98fh-3x25-7rmr, MINI-98w3-8mh5-39m4, MINI-994r-cqjm-4w3v, MINI-9r9q-3pp9-rm9v, MINI-c7vj-q6j2-6qrj, MINI-cpvv-phjv-8p3h, MINI-f3cj-fc73-46c5, MINI-f98j-4736-vmjh, MINI-ffr9-xf28-5v73, MINI-fqv3-fhg8-x5h4, MINI-fvf2-prhg-545v, MINI-g299-w585-x845, MINI-g2hq-8pvm-587q, MINI-g4h6-8466-6pfr, MINI-g7xv-gqph-v3fw, MINI-gjhq-fp8m-x9cq, MINI-gmhg-h59g-grgr, MINI-grmc-g52j-xpc7, MINI-j34p-mw47-f9cq, MINI-j7mm-fgxw-xmcr, MINI-jfwg-r447-fp5v, MINI-jhmx-fq28-pch5, MINI-jpwp-895w-wwp6, MINI-jxmq-jc82-jhgg, MINI-m3f7-fgvx-cm8j, MINI-p53m-wx4w-4w7r, MINI-pmff-frq2-3vf4, MINI-ppm4-4736-hfqc, MINI-q97x-7r6x-5r2f, MINI-qfhc-rxxw-8wgr, MINI-qmm3-j99w-h34x, MINI-qxvr-j374-9wvj, MINI-qxwm-73jq-j494, MINI-r5hg-5rf8-w4j8, MINI-rcwp-c54f-f4gh, MINI-rfg5-p3v2-jq7h, MINI-rr86-h535-cvx5, MINI-v33g-547h-cvg9, MINI-v36j-hxhr-vqr8, MINI-v3w8-p678-qpvv, MINI-v4m3-m825-hgm3, MINI-v6fg-5mvh-xmp3, MINI-v6rf-52mc-jvqj, MINI-v823-xcgj-74j8, MINI-vm33-g4vc-35h6, MINI-vmjr-4f68-45vh, MINI-vqhq-chgp-8x88, MINI-w2j6-w6x3-r9xf, MINI-w428-rrg4-r2g6, MINI-w5cf-rcxh-7m7g, MINI-wmgg-6xg2-689q, MINI-x5fm-2f68-jg4c, MINI-x88g-qww6-7gx4, MINI-xxj6-59g8-ccpw, ROOT-APP-MAVEN-CVE-2026-56819, UBUNTU-CVE-2026-56819 ## What is CVE-2026-56819? CVE-2026-56819 is a high-severity denial of service vulnerability in Netty Netty, published on 21 Jul 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. In versions 4.2.0.Final through 4.2.15.Final and 4.1.0.Final through 4.1.135.Final, a remote unauthenticated peer can leak one direct `ByteBuf` per HTTP/2 `DATA` frame in applications that enable HTTP/2 content decompression via `DelegatingDecompressorFrameListener`. When a `DATA` frame is processed for a stream whose decompressor has already been closed, `Http2Decompressor.decompress(...)` calls `decompressor.writeInbound(data.retain())` and does not release the retained buffer on the error path, eventually exhausting direct memory and crashing the JVM. This issue is fixed in versions 4.1.136.Final and 4.2.16.Final. Weakness: CWE-401 (Missing Release of Memory after Effective Lifetime), CWE-400 (Uncontrolled Resource Consumption) ## Which versions are affected by CVE-2026-56819? 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 | From 4.1.0.Final | 4.1.136.Final | | `io.netty:netty-codec-http2` | Maven | From 4.1.0.Final | 4.1.136.Final | | `io.netty:netty-codec-http2` | Maven | From 4.2.0 | 4.2.16.Final | | `io.netty:netty-codec-http2` | Maven | From 4.2.0 | 4.2.16.Final | Products: Netty Netty. ## How do I fix CVE-2026-56819? Upgrade io.netty:netty-codec-http2 to a fixed version for your release line: 4.1.136.Final or 4.2.16.Final. ## Is CVE-2026-56819 being exploited? It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-56819 exists. Public exploit code: - CVE-2025-55163 / CVE-2026-56819: offline checker for the 7 netty-codec-http2 CVEs. Tells you which ones you are exposed to, and the one version that fixes all seven (4.1.136.Final / 4.2.16.Final) - written on none of the advisories. Does not scan pom.xml on purpose: WebFlux pulls it in transitively. (github_poc): https://github.com/xiaoqiMikko/netty-http2-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-2026-56819 and fix it if it is affected. What it is: CVE-2026-56819 is a high-severity denial of service vulnerability in Netty Netty, published on 21 Jul 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-2026-56819 exists. Affected packages and fixed versions: - io.netty:netty-codec-http2 (Maven): affected from 4.1.0.Final; fixed in 4.1.136.Final - io.netty:netty-codec-http2 (Maven): affected from 4.1.0.Final; fixed in 4.1.136.Final - io.netty:netty-codec-http2 (Maven): affected from 4.2.0; fixed in 4.2.16.Final - io.netty:netty-codec-http2 (Maven): affected from 4.2.0; 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-2026-56819/ (Markdown: https://insights.sbomify.com/CVE-2026-56819/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-56819 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-56819 - OSV: https://osv.dev/vulnerability/CVE-2026-56819 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-56819/ Summaries are generated and may contain mistakes; the official description above is the record.