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.
| Product | Vendor Advisory | Solution File | Added | Published |
|---|---|---|---|---|
| Alma_linux | — | Upgrade mod_http2 | May 8, 2024 | Oct 23, 2023 |
| Alpine Linux | — | Upgrade apache2 | Mar 26, 2024 | Oct 23, 2023 |
| Amazon Linux Ami 2 | — | Upgrade httpdUpgrade httpd-toolsUpgrade mod_mdUpgrade httpd-manualUpgrade mod_sessionUpgrade mod_ldapUpgrade mod_sslUpgrade httpd-debuginfoUpgrade httpd-develUpgrade mod_proxy_htmlUpgrade httpd-filesystem | Nov 3, 2023 | Oct 23, 2023 |
| Amazon_linux | — | Upgrade httpd24 | Nov 4, 2023 | Oct 23, 2023 |
| Amazon_linux_2023 | — | Upgrade mod_sslUpgrade httpd-filesystemUpgrade mod_luaUpgrade mod_proxy_html-debuginfoUpgrade mod_session-debuginfoUpgrade httpd-debuginfoUpgrade httpd-tools-debuginfoUpgrade mod_proxy_htmlUpgrade mod_ldapUpgrade mod_sessionUpgrade httpd-coreUpgrade httpd-debugsourceUpgrade httpd-develUpgrade httpdUpgrade mod_lua-debuginfoUpgrade httpd-toolsUpgrade httpd-core-debuginfoUpgrade mod_ssl-debuginfoUpgrade mod_ldap-debuginfoUpgrade httpd-manual | Feb 17, 2025 | Oct 10, 2023 |
| Apache Httpd | — | Upgrade to the latest version of Apache HTTPD | Nov 29, 2023 | Oct 23, 2023 |
| Debian | — | Upgrade apache2 | Apr 18, 2024 | Oct 23, 2023 |
| Freebsd | — | Upgrade apache24Upgrade varnish7 | Dec 10, 2025 | Oct 19, 2023 |
| Gentoo Linux | — | Upgrade www-servers/apache. | Aug 16, 2026 | Aug 13, 2026 |
| Oracle_linux | — | Upgrade mod_http2 | May 8, 2024 | Oct 10, 2023 |
| Redhat_linux | — | Upgrade mod_http2-debuginfoUpgrade mod_http2Upgrade mod_http2-debugsource | May 1, 2024 | Oct 23, 2023 |
| Ubuntu | — | Upgrade apache2 | Nov 23, 2023 | Oct 23, 2023 |
| Vmware Photon_os | — | Use 'tdnf update' to upgrade all packages to the latest version. | Jan 20, 2025 | Oct 23, 2023 |
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