An emergency update has been released for Apache http server 2.4.50, which fixes an actively exploited 0-day vulnerability (CVE-2021-41773) that allows access to files from areas outside the web root directory. This vulnerability enables arbitrary system files and web script source codes, readable by the user under which the http server is running, to be uploaded. Developers were notified of the problem on September 17, but could only release the update today after cases of the vulnerability being used to attack websites were recorded online.
The danger of the vulnerability is somewhat mitigated by the fact that the issue only appears in the recently released version 2.4.49 and does not affect all earlier releases. Stable branches of conservative server distributions have not yet used the 2.4.49 release (Debian, RHEL, Ubuntu, SUSE), but the problem has affected continuously updated distributions such as Fedora, Arch Linux, and Gentoo, as well as FreeBSD ports.
Podatność została spowodowana błędem wprowadzonego podczas przeróbki kodu, który miał na celu normalizację ścieżek w URI, przez co zakodowany za pomocą sekwencji "" znak kropki w ścieżce nie był normalizowany, jeśli poprzedzała go inna kropka. W ten sposób możliwe stało się wstrzykiwanie nieoczyszczonych symboli "..\/" do wynikowej ścieżki poprzez wskazanie w zapytaniu sekwencji ".\/". Na przykład zapytanie w postaci "https:\/\/example.com\/cgi-bin\/.\/.\/.\/.\/etc\/passwd" lub "https:\/\/example.com\/cgi-bin\/.\/\/\\/\\/etc\/hosts" pozwalało uzyskać zawartość pliku "\/etc\/passwd".
The problem does not manifest if access to directories is explicitly denied by the 'require all denied' setting. For partial protection, you can specify in the configuration file: require all denied
In Apache httpd version 2.4.50, another vulnerability (CVE-2021-41524) affecting the module implementing the HTTP/2 protocol has also been fixed. This vulnerability allowed sending specially crafted requests to trigger a null pointer dereference and crash the process. This vulnerability also only manifests in version 2.4.49. As a workaround for protection, you can disable HTTP/2 support.
Źródło: opennet.ru
