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Vulnerability Intelligence

CVE-2023-43622

HighPublic exploit

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.

Published Nov 27, 2023 · Updated Oct 8, 2026 · Also known as ALPINE-CVE-2023-43622, BIT-apache-2023-43622, DEBIAN-CVE-2023-43622, UBUNTU-CVE-2023-43622

Key Facts

Patch immediately
  • CVE-2023-43622 is a high-severity vulnerability (CVSS 7.5 v3.1) affecting HTTP Server (Apache), apache2 (alpine), apache (bitnami) and 22 more products.
  • It is not listed in any known-exploited vulnerabilities catalog. Public exploit code is available.
  • EPSS estimates a 71% probability of exploitation in the next 30 days.
  • Fixed versions are available, including apache 2.4.58, HTTP Server 2.4.58, apache2 2.4.41-4ubuntu3.15.
  • Brandefense priority: patch immediately, because it is very likely to be exploited soon.

CVSS v3.1

7.5

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

EPSS (30-day exploit likelihood)

71%

Higher than 99.3% of all scored CVEs

Exploited in the wild

No known

Not in a known-exploited catalog

Public exploit code

Available

Proof-of-concept or weaponized module

Get the full CVE-2023-43622 brief as a PDF

Every affected product and fixed release, exploitation status and a first 24 hours response checklist, emailed within minutes.

Description

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.

Affected Products

71 affected entries in total
ProductAffected versionsFixed in
HTTP ServerApache>= 2.4.552.4.58
apache2alpineSee advisory2.4.58-r0
apachebitnami>= 2.4.552.4.58
rootio-apache2rootioSee advisory2.4.59-1~deb12u1
mod_http2almaSee advisory2.0.26-1.el9
20 more affected products in the full CVE brief

Patched Releases

apache

2.4.58

HTTP Server

2.4.58

apache2

2.4.41-4ubuntu3.15, 2.4.52-1ubuntu4.7, 2.4.58-1, 2.4.58-1.1, 2.4.58-r0, 2.4.59-1~deb11u1, 2.4.59-1~deb12u1

httpd

2.4.58-1, 2.4.58-1.amzn2, 2.4.58-1.amzn2023, 2.4.58-1.ph3, 2.4.58-1.ph4

httpd-core

2.4.58-1.amzn2023

httpd-devel

2.4.58-1.amzn2, 2.4.58-1.amzn2023, 2.4.58-1.ph4

httpd-docs

2.4.58-1.ph4

httpd-filesystem

2.4.58-1.amzn2, 2.4.58-1.amzn2023

httpd-manual

2.4.58-1.amzn2, 2.4.58-1.amzn2023

httpd-tools

2.4.58-1.amzn2, 2.4.58-1.amzn2023, 2.4.58-1.ph4

httpd24

2.4.58-1.101.amzn1

httpd24-devel

2.4.58-1.101.amzn1

httpd24-manual

2.4.58-1.101.amzn1

httpd24-tools

2.4.58-1.101.amzn1

mod_http2

0:2.0.26-1.el9, 2.0.26-1.el9, 2.0.29-3

mod_ldap

2.4.58-1.amzn2, 2.4.58-1.amzn2023

mod_lua

2.4.58-1.amzn2023

mod_md

2.4.58-1.amzn2

mod_proxy_html

1:2.4.58-1.amzn2, 1:2.4.58-1.amzn2023

mod_session

2.4.58-1.amzn2, 2.4.58-1.amzn2023

mod_ssl

1:2.4.58-1.amzn2, 1:2.4.58-1.amzn2023

mod24_ldap

2.4.58-1.101.amzn1

mod24_md

2.4.58-1.101.amzn1

mod24_proxy_html

1:2.4.58-1.101.amzn1

mod24_session

2.4.58-1.101.amzn1

Timeline

  1. Publicly disclosed

    Nov 27, 2023

  2. Last updated

    Oct 8, 2026

Weakness Type

  • CWE-400 Uncontrolled Resource Consumption

References

10 more references in the full CVE brief

FAQ

Common Questions.

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