CVE-2026-48059
CVE-2026-48059 is a CWE-401 vulnerability in io.netty:netty-codec-haproxy. O3 Security confirms whether CVE-2026-48059 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Netty HAProxy: Unbalanced Reference Count in Nested PP2_TYPE_SSL TLV Parsing Leads to Memory Exhaustion
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-48059.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
io.netty:netty-codec-haproxy☕io.netty:netty-codec-haproxyReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
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, the HAProxy PROXY protocol v2 codec in netty leaks native or heap memory on every connection when a client sends a syntactically valid header containing nested PP2_TYPE_SSL TLVs (type-length-value records) at depth two or greater. The leak occurs on the successful parse path — no exception is thrown, the message fires downstream, the decoder removes itself, and the application releases the HAProxyMessage normally. Yet the underlying cumulation buffer (a pooled, potentially direct ByteBuf allocated by the channel) remains permanently pinned. Versions 4.1.135.Final and 4.2.15.Final patch the issue.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | io.netty:netty-codec-haproxy | ≥ 4.2.0.Final&&< 4.2.15.Final | 4.2.15.Final |
| ☕Maven | io.netty:netty-codec-haproxy | all versions | 4.1.135.Final |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for io.netty:netty-codec-haproxy. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update io.netty:netty-codec-haproxy to 4.2.15.Final or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-48059 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-48059 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-48059. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
This is an Important flaw in the Netty HAProxy PROXY protocol v2 codec, which can lead to a denial of service. A remote attacker can trigger a memory leak by sending a specially crafted HAProxy PROXY protocol v2 header with deeply nested SSL TLV records, causing resource exhaustion in affected Red Hat products that…
Frequently Asked Questions
Is CVE-2026-48059 in your dependencies?
O3 detects CVE-2026-48059 across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.