A flaw was found in rubygem-puma. A poorly-behaved client could use keepalive requests to monopolize Puma's reactor and create a denial of service attack. If more keepalive connections to Puma are opened than there are threads available, additional connections will wait permanently if the attacker sends requests frequently enough.

Impact

By using an invalid transfer-encoding header, an attacker could smuggle an HTTP response.

Originally reported by @ZeddYu, who has our thanks for the detailed report.

Patches

The problem has been fixed in Puma 3.12.5 and Puma 4.3.4.

For more information

If you have any questions or comments about this advisory:

Open an issue in Puma See our security policy

Impact This is a similar but different vulnerability to the one patched in 3.12.5 and 4.3.4.

A client could smuggle a request through a proxy, causing the proxy to send a response back to another unknown client.

If the proxy uses persistent connections and the client adds another request in via HTTP pipelining, the proxy may mistake it as the first request's body. Puma, however, would see it as two requests, and when processing the second request, send back a response that the proxy does not expect. If the proxy has reused the persistent connection to Puma to send another request for a different client, the second response from the first client will be sent to the second client.

Patches

The problem has been fixed in Puma 3.12.6 and Puma 4.3.5.

For more information

If you have any questions or comments about this advisory:

Open an issue in Puma See our security policy