Summary
Yamux vulnerable to remote Panic via malformed WindowUpdate credit
Sumary
The Rust implementation of Yamux accepts WindowUpdate credit values from the remote peer and applies them to per-stream send-window state.
A specially crafted WindowUpdate can cause arithmetic overflow in send-window accounting, which triggers a panic in the connection state machine. This is remotely reachable over a normal network connection and does not require authentication.
Attack Scenario
An attacker that can establish a Yamux session with a target node can crash the target by sending two validly encoded Yamux frames:
- Open a stream (e.g. DATA + SYN) so the stream exists with initial send-window state (
DEFAULT_CREDIT). - Send a WindowUpdate on that stream with a very large credit value (e.g. 0xFFFF_0000) such that adding credit to the current send-window overflows u32.
Impact
Remote unauthenticated denial of service.
An attacker can repeatedly trigger panics by reconnecting and replaying the crafted frame sequence.
An arithmetic operation produces a value that exceeds the integer type's maximum, causing it to wrap to an unexpected small value. Typical impact: incorrect size calculations leading to heap overflows or logic errors.
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.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
Users should upgrade to yamux v0.13.9
This vulnerability was originally submitted by @revofusion to the Ethereum Foundation bug bounty program
Frequently Asked Questions
- What is CVE-2026-31814? CVE-2026-31814 is a high-severity integer overflow or wraparound vulnerability in yamux (rust), affecting versions >= 0.13.0, < 0.13.9. It is fixed in 0.13.9. An arithmetic operation produces a value that exceeds the integer type's maximum, causing it to wrap to an unexpected small value.
- Which versions of yamux are affected by CVE-2026-31814? yamux (rust) versions >= 0.13.0, < 0.13.9 is affected.
- Is there a fix for CVE-2026-31814? Yes. CVE-2026-31814 is fixed in 0.13.9. Upgrade to this version or later.
- Is CVE-2026-31814 exploitable, and should I be worried? Whether CVE-2026-31814 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-2026-31814 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-2026-31814? Upgrade
yamuxto 0.13.9 or later.