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GHSA-85rg-p3fr-xc2f

HighCVSS 8.6 / 10
Published Jul 28, 2026·Last modified Jul 28, 2026
Affected Components(0)

No affected components available

Description

Impact

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).

Patches

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

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)
Risk Scores
Base Score
8.6

The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The vulnerability can affect other systems as well, not just the initial system. There is a high impact on the availability of the system.

Threat Intelligence
7.9

Exploitation activity has been observed. Apply available patches or mitigations urgently.

EPSS
0.26%

The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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High severity
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