This vulnerability is related to CVE-2019-16770.
Impact
The fix for CVE-2019-16770 was incomplete. The original fix only protected existing connections that had already been accepted from having their requests starved by greedy persistent-connections saturating all threads in the same process. However, new connections may still be starved by greedy persistent-connections saturating all threads in all processes in the cluster.
A puma server which received more concurrent keep-alive connections than the server had threads in its threadpool would service only a subset of connections, denying service to the unserved connections.
Patches
This problem has been fixed in puma 4.3.8 and 5.3.1.
Workarounds
Setting queue_requests false also fixes the issue. This is not advised when using puma without a reverse proxy, such as nginx or apache, because you will open yourself to slow client attacks (e.g. slowloris).
The fix is very small. A git patch is available here for those using unsupported versions of Puma.
For more information
If you have any questions or comments about this advisory:
Acknowledgements
Thank you to @MSP-Greg, @wjordan and @evanphx for their review on this issue.
Thank you to @ioquatix for providing a modified fork of wrk which made debugging this issue much easier.
References
This vulnerability is related to CVE-2019-16770.
Impact
The fix for CVE-2019-16770 was incomplete. The original fix only protected existing connections that had already been accepted from having their requests starved by greedy persistent-connections saturating all threads in the same process. However, new connections may still be starved by greedy persistent-connections saturating all threads in all processes in the cluster.
A
pumaserver which received more concurrentkeep-aliveconnections than the server had threads in its threadpool would service only a subset of connections, denying service to the unserved connections.Patches
This problem has been fixed in
puma4.3.8 and 5.3.1.Workarounds
Setting
queue_requests falsealso fixes the issue. This is not advised when usingpumawithout a reverse proxy, such asnginxorapache, because you will open yourself to slow client attacks (e.g. slowloris).The fix is very small. A git patch is available here for those using unsupported versions of Puma.
For more information
If you have any questions or comments about this advisory:
Acknowledgements
Thank you to @MSP-Greg, @wjordan and @evanphx for their review on this issue.
Thank you to @ioquatix for providing a modified fork of
wrkwhich made debugging this issue much easier.References