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Date: Thu, 19 Oct 2023 09:40:49 +0000
From: Stefan Eissing <>
Subject: CVE-2023-43622: Apache HTTP Server: DoS in HTTP/2 with initial
 windows size 0 

Severity: low

Affected versions:

- Apache HTTP Server 2.4.55 through 2.4.57


An attacker, opening a HTTP/2 connection with an initial window size of 0, was able to block handling of that connection indefinitely in Apache HTTP Server. This could be used to exhaust worker resources in the server, similar to the well known "slow loris" attack pattern.
This has been fixed in version 2.4.58, so that such connection are terminated properly after the configured connection timeout.

This issue affects Apache HTTP Server: from 2.4.55 through 2.4.57.

Users are recommended to upgrade to version 2.4.58, which fixes the issue.


Prof. Sven Dietrich (City University of New York) (finder)
Isa Jafarov (City University of New York) (finder)
Prof. Heejo Lee (Korea University) (finder)
Choongin Lee (Korea University) (finder)



2023-09-15: reported

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