Google Project Zero expert found 3 flaws in Apache Web Server

Administrators of servers running Apache have to update their installs immediately to fix multiple vulnerabilities disclosed by a Google researcher.

Apache Foundation released the 2.4.46 version to address three flaws affecting its web server software that could be potentially exploited by attackers, under specific conditions, to execute arbitrary code or to trigger a DoS condition by crashing the server.

The three vulnerabilities, tracked as CVE-2020-9490, CVE-2020-11984, CVE-2020-11993, were reported by Google Project Zero researcher Felix Wilhelm.

“Apache’s mod_http2 module supports a feature called push diary that keeps track of all resources already pushed over a single HTTP/2 connection. To avoid unnecessary pushes on new connections, clients can initialize or replace the active push diary by sending a base64-encoded diary in the ‘Cache-Digest’ header (this feature is based on an abandoned
IETF draft described in https://datatracker.ietf.org/doc/draft-ietf-httpbis-cache-digest/).” reads the analysis published by Google.

“Unfortunately, the current stable release (2.4.43) incorrectly parses diary digests which can trigger a memory corruption through a wild memmove call.”

The most severe flaw, tracked as CVE-2020-9490, resides in the HTTP/2 module.

An attacker could cause a memory corruption condition by using a specially crafted ‘Cache-Digest’ header leading to a crash and denial of service.

“A specially crafted value for the ‘Cache-Digest’ header in a HTTP/2 request would result in a crash when the server actually tries to HTTP/2 PUSH a resource afterwards.” reported Google.

The second vulnerability, tracked as CVE-2020-11984, is a buffer overflow issue impacting the “mod_uwsgi” module that could lead to remote code execution.

The flaw could potentially allow an attacker to view, change, or delete sensitive data depending on the privileges associated with an application running on the server.

“The modules mod_proxy_ajp and mod_proxy_http did not always close the connection to the back end server when necessary as part of error handling. This could lead to an information disclosure due to a response mixup between users.” reads the advisory published by Apache.

The third flaw, tracked as CVE-2020-11993, is exploitable only when debugging is enabled in the “mod_http2” module, causing logging statements to be made on the wrong connection and resulting in memory corruption due to the concurrent log pool usage.

At the time, Apache Foundation is not aware of attacks in the wild exploiting the vulnerabilities. Administrators are recommended to patch their installations immediately.

Pierluigi Paganini

(SecurityAffairs – hacking, Apache)