CVE-2026-54609

QTINeon has unauthenticated relay-to-host amplification via unbounded RECONNECT_REQUEST forwarding

Workarounds

Operators can partially mitigate by placing the relay behind a network-level filter that drops packets with spoofed source addresses (BCP38/uRPF). This does not address the missing pendingReconnects size cap or the rateLimiters.clear() issue but eliminates the amplification path in most deployment environments.

References

• PROTOCOL.md, reconnect flow
• ARCHITECTURE.md, reconnect handshake detail (step 4 describes the unbounded put)

The relay's reconnect handler forwards every RECONNECT_REQUEST to the host without deduplication or a size cap on the pendingReconnects map, unlike the connect flow which guards against this with maxPendingConnections. An unauthenticated attacker who knows a valid session ID can send RECONNECT_REQUEST packets from many spoofed source addresses; each packet that passes the session lookup is forwarded to the host as a new reconnect attempt. Because the per-source rate limiter assigns a fresh token bucket to each spoofed IP, it provides no protection. The host receives one forwarded packet per spoofed source per cleanup cycle, making the relay an amplification vector for denial-of-service against the host. The host's real address is never exposed to clients by design, so this is the primary viable DoS path against it. A secondary issue: once more than maxRateLimiters spoofed IPs are seen, performCleanup calls rateLimiters.clear(), resetting rate limit state for all sources including legitimate ones.

Affected: NeonRelay in all three implementations (Java, Python, TypeScript).

Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.

CVE-2026-54609 has a CVSS score of 8.6 (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. No fixed version is listed yet, so configuration controls and monitoring matter more in the interim.

Kodem intelligence

Already deployed Kodem?

Not yet patched. Fix consists of three changes to handleReconnectRequest in each implementation:

1. Reject the request if pendingReconnects.size() >= maxPendingConnections (mirrors the existing connect-flow guard)
2. Only forward to the host if the sessionId:clientId key is not already present in pendingReconnects, the map entry can still be updated with the new source address, but the host only needs to validate once per slot
3. In performCleanup, evict throttled entries before falling back to rateLimiters.clear() to avoid resetting legitimate sources' rate limit state

1. What is CVE-2026-54609? CVE-2026-54609 is a high-severity uncontrolled resource consumption vulnerability in com.quietterminal:qti-neon (maven), affecting versions = 1.0.0. No fixed version is listed yet. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
2. How severe is CVE-2026-54609? CVE-2026-54609 has a CVSS score of 8.6 (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.
3. Which packages are affected by CVE-2026-54609?
   • com.quietterminal:qti-neon (maven) (versions = 1.0.0)
   • qti-neon (pip) (versions = 1.0.0)
4. Is there a fix for CVE-2026-54609? No fixed version is listed for CVE-2026-54609 yet. Monitor the advisory for updates and apply mitigations in the interim.
5. Is CVE-2026-54609 exploitable, and should I be worried? Whether CVE-2026-54609 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
6. What actually determines whether CVE-2026-54609 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.
7. How do I fix CVE-2026-54609? No fixed version is listed yet. In the interim: Apply input size limits and request rate limiting. Reject input that exceeds reasonable bounds before processing begins.