CVE-2021-29509
Description
Puma is a concurrent HTTP 1.1 server for Ruby/Rack applications. 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. This problem has been fixed in `puma` 4.3.8 and 5.3.1. 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 and a git patch is available for those using unsupported versions of Puma.
References
CvssV3 impact
BaseSeverity | HIGH |
ConfidentialityImpact | NONE |
AttackComplexity | LOW |
Scope | UNCHANGED |
AttackVector | NETWORK |
AvailabilityImpact | HIGH |
IntegrityImpact | NONE |
PrivilegesRequired | NONE |
BaseScore | 7.5 |
VectorString | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
Version | 3.1 |
UserInteraction | NONE |
CvssV2 impact
AccessComplexity | LOW |
ConfidentialityImpact | NONE |
AvailabilityImpact | PARTIAL |
IntegrityImpact | NONE |
BaseScore | 5 |
VectorString | AV:N/AC:L/Au:N/C:N/I:N/A:P |
Version | 2.0 |
AccessVector | NETWORK |
Authentication | NONE |