Flooding attack against synchronising keyservers

Andrew Gallagher andrewg at andrewg.com
Mon Mar 27 19:47:00 CEST 2023

Hi, everyone.

The synchronising keyserver network has been under an intermittent flooding attack for the past five days, resulting in the addition of approximately 3 million obviously-fake OpenPGP keys to the SKS dataset. The fake keys are currently being submitted multiple times per second via a large number of Tor exit relays, making them difficult to block using normal abuse mitigations. If unaddressed, this will eventually fill up the disk of all public synchronising servers.

Effective immediately, pgpkeys.eu has been temporarily disconnected from all its peers, and is blocking all key submissions. It will remain available for key lookups but will not allow key updates while the flooding attack continues.

I strongly recommend that other keyserver operators take similar measures, until a more permanent solution can be deployed.


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