CVE Vulnerabilities

CVE-2021-32785

Use of Externally-Controlled Format String

Published: Jul 22, 2021 | Modified: Nov 21, 2024
CVSS 3.x
7.5
HIGH
Source:
NVD
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS 2.x
4.3 MEDIUM
AV:N/AC:M/Au:N/C:N/I:N/A:P
RedHat/V2
RedHat/V3
7.5 MODERATE
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Ubuntu
MEDIUM

mod_auth_openidc is an authentication/authorization module for the Apache 2.x HTTP server that functions as an OpenID Connect Relying Party, authenticating users against an OpenID Connect Provider. When mod_auth_openidc versions prior to 2.4.9 are configured to use an unencrypted Redis cache (OIDCCacheEncrypt off, OIDCSessionType server-cache, OIDCCacheType redis), mod_auth_openidc wrongly performed argument interpolation before passing Redis requests to hiredis, which would perform it again and lead to an uncontrolled format string bug. Initial assessment shows that this bug does not appear to allow gaining arbitrary code execution, but can reliably provoke a denial of service by repeatedly crashing the Apache workers. This bug has been corrected in version 2.4.9 by performing argument interpolation only once, using the hiredis API. As a workaround, this vulnerability can be mitigated by setting OIDCCacheEncrypt to on, as cache keys are cryptographically hashed before use when this option is enabled.

Weakness

The product uses a function that accepts a format string as an argument, but the format string originates from an external source.

Affected Software

Name Vendor Start Version End Version
Mod_auth_openidc Openidc * 2.4.9 (excluding)
Libapache2-mod-auth-openidc Ubuntu bionic *
Libapache2-mod-auth-openidc Ubuntu esm-apps/bionic *
Libapache2-mod-auth-openidc Ubuntu esm-apps/focal *
Libapache2-mod-auth-openidc Ubuntu focal *
Libapache2-mod-auth-openidc Ubuntu hirsute *
Libapache2-mod-auth-openidc Ubuntu trusty *
Libapache2-mod-auth-openidc Ubuntu upstream *
Libapache2-mod-auth-openidc Ubuntu xenial *

Potential Mitigations

References