Add handshakes.max_rate to limit new handshakes per second - #1643
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Nebula is vulnerable to DoS via handshake flooding since each incoming handshake performs expensive DH operations. This adds a token bucket rate limiter to the handshake manager that caps both inbound and outbound new handshakes per second. When the limit is reached, new handshakes are silently dropped and counted via the handshake_manager.rate_limited metric. Configured via handshakes.max_rate (default 0 = unlimited). Co-Authored-By: Claude <svc-devxp-claude@slack-corp.com>
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JackDoan
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| # handshakes count against this limit. Once the limit is reached, new handshakes are dropped | ||
| # until the next second. A value of 0 means unlimited (default). | ||
| # This is useful for preventing DoS attacks that attempt to exhaust CPU with handshake crypto. | ||
| # Running `openssl speed ecdhp256` on your hardware can be a good rule of thumb for choosing |
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might note that this is single-core, and that you may wish to scale this number per routine
JackDoan
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Apr 10, 2026
| return hh.hostinfo | ||
| } | ||
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| // Check rate limit for new outbound handshakes |
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from a DOS perspective, does it make sense to rate-limit outbound handshakes?
JackDoan
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| hm.metricRateLimited.Inc(1) | ||
| hm.l.WithField("vpnAddr", vpnAddr).Debug("Handshake rate limit reached, dropping outbound handshake") | ||
| hm.Unlock() | ||
| return nil |
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historically this has always been non-nil, is there anywhere that barfs bc we changed that? If we do decide to ratelimit outbounds, I'd have a slight preference to refactor this to be (*HostInfo, error) I think
Remove rate limiting from StartHandshake (outbound) since DoS protection only needs to limit inbound handshakes. This also avoids returning nil from StartHandshake which historically always returned non-nil. Update config comment to note openssl speed is single-core and suggest scaling by routines. Co-Authored-By: Claude <svc-devxp-claude@slack-corp.com>
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Nebula is vulnerable to DoS via handshake flooding since each incoming
handshake performs expensive DH operations. This adds a token bucket
rate limiter to the handshake manager that caps both inbound and
outbound new handshakes per second. When the limit is reached, new
handshakes are silently dropped and counted via the
handshake_manager.rate_limited metric.
Configured via handshakes.max_rate (default 0 = unlimited).
Co-Authored-By: Claude svc-devxp-claude@slack-corp.com