CVE-2021-21294 Information

Description

Http4s (http4s-blaze-server) is a minimal idiomatic Scala interface for HTTP services. Http4s before versions 0.21.17 0.22.0-M2 and 1.0.0-M14 have a vulnerability which can lead to a denial-of-service. Blaze-core a library underlying http4s-blaze-server accepts connections unboundedly on its selector pool. This has the net effect of amplifying degradation in services that are unable to handle their current request load since incoming connections are still accepted and added to an unbounded queue. Each connection allocates a socket handle which drains a scarce OS resource. This can also confound higher level circuit breakers which work based on detecting failed connections. http4s provides a general \MaxActiveRequests\ middleware mechanism for limiting open connections but it is enforced inside the Blaze accept loop after the connection is accepted and the socket opened. Thus the limit only prevents the number of connections which can be simultaneously processed not the number of connections which can be held open. In 0.21.17 0.22.0-M2 and 1.0.0-M14 a new \maxConnections\ property with a default value of 1024 has been added to the BlazeServerBuilder. Setting the value to a negative number restores unbounded behavior but is strongly disrecommended. The NIO2 backend does not respect maxConnections. Its use is now deprecated in http4s-0.21 and the option is removed altogether starting in http4s-0.22. There are several possible workarounds described in the refrenced GitHub Advisory GHSA-xhv5-w9c5-2r2w.

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Reference

https://github.com/http4s/http4s/commit/987d6589ef79545b9bb2324ac4bdebf82d9a0171 https://github.com/http4s/http4s/security/advisories/GHSA-xhv5-w9c5-2r2w https://github.com/http4s/blaze/security/advisories/GHSA-xmw9-q7x9-j5qc

Attack Complexity

LOW

Privileges Required

NONE

User Interaction Required

NONE

Scope

NONE

Confidentiality Impact

UNCHANGED

Integrity Impact

NONE

Availability Impact

NONE

Base Score

HIGH

Base Severity

7.5