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CVE-2021-21294— Unbounded connection acceptance in http4s-blaze-server

Quick assessment

Affected
http4s http4s
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Http4s Blaze是Http4s组织的一个基于java的用于处理网络流的NIO代码库。 Http4s Blaze 存在安全漏洞，该漏洞源于选择器池上无限制地接受连接。以下产品及版本受到影响：Http4s before versions 0.21.17, 0.22.0-M2, and 1.0.0-M14。

CVSS 7.5 · High EPSS 2.15% · P81
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I. Basic Information for CVE-2021-21294

Vulnerability Information
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Vulnerability Title
Unbounded connection acceptance in http4s-blaze-server
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
未加控制的资源消耗(资源穷尽)
Source: CVE Program / CVE List V5
Vulnerability Title
Http4s Blaze 资源管理错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Http4s Blaze是Http4s组织的一个基于java的用于处理网络流的NIO代码库。 Http4s Blaze 存在安全漏洞，该漏洞源于选择器池上无限制地接受连接。以下产品及版本受到影响：Http4s before versions 0.21.17, 0.22.0-M2, and 1.0.0-M14。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
http4s http4s < 0.21.17 -

II. Public POCs for CVE-2021-21294

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III. Intelligence Information for CVE-2021-21294

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Patches & Fixes for CVE-2021-21294 (1)

Vendor Advisories for CVE-2021-21294 (1)

IV. Related Vulnerabilities

Same product: http4s
Same vendor: http4s
Same weakness: CWE-400

V. Comments for CVE-2021-21294

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