Summary
Netty: Memory Exhaustion in SctpMessageCompletionHandler
SctpMessageCompletionHandler does not limit the total size of buffered fragments, allowing an unauthenticated attacker to cause an OutOfMemoryError by sending large SCTP fragments.
Details
io.netty.handler.codec.sctp.SctpMessageCompletionHandler buffers fragments for incomplete SCTP messages. The fix for CVE-2026-46340 fixed unbounded memory growth by introducing limits on the number of concurrent incomplete messages (maxIncompleteSctpMessages) and the number of fragments per message (maxFragments).
While the count of fragments is now bounded, the handler still does not enforce a maximum size in bytes.
With the default limits of 128 messages and 128 fragments, and a typical max SCTP chunk size of 64KB, an attacker can consume up to ~1GB per connection. By opening a small number of concurrent connections, an attacker can easily exhaust the server's memory, causing an OutOfMemoryError.
Impact
Memory Exhaustion. Any application using Netty's SCTP transport with SctpMessageCompletionHandler is impacted.
Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.
CVE-2026-59902 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.2.17.Final, 4.1.137.Final); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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io.netty:netty-transport-sctp to 4.2.17.Final or later; io.netty:netty-transport-sctp to 4.1.137.Final or later
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-59902? CVE-2026-59902 is a high-severity uncontrolled resource consumption vulnerability in io.netty:netty-transport-sctp (maven), affecting versions >= 4.2.0.Final, <= 4.2.16.Final. It is fixed in 4.2.17.Final, 4.1.137.Final. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
- How severe is CVE-2026-59902? CVE-2026-59902 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of io.netty:netty-transport-sctp are affected by CVE-2026-59902? io.netty:netty-transport-sctp (maven) versions >= 4.2.0.Final, <= 4.2.16.Final is affected.
- Is there a fix for CVE-2026-59902? Yes. CVE-2026-59902 is fixed in 4.2.17.Final, 4.1.137.Final. Upgrade to this version or later.
- Is CVE-2026-59902 exploitable, and should I be worried? Whether CVE-2026-59902 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-59902 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-59902?
- Upgrade
io.netty:netty-transport-sctpto 4.2.17.Final or later - Upgrade
io.netty:netty-transport-sctpto 4.1.137.Final or later
- Upgrade