Bug 1986100 (CVE-2021-32785)

Summary:	CVE-2021-32785 mod_auth_openidc: format string bug in the Redis cache implementation
Product:	[Other] Security Response	Reporter:	Guilherme de Almeida Suckevicz <gsuckevi>
Component:	vulnerability	Assignee:	Red Hat Product Security <security-response-team>
Status:	CLOSED NOTABUG	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	jhrozek, puiterwijk, spoore, thalman
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:	mod_auth_openidc 2.4.9	Doc Type:	If docs needed, set a value
Doc Text:	A flaw was found in mod_auth_openidc. When mod_auth_openidc is configured to use unencrypted Redis cache it is possible to trigger a format string bug that could be used by a remote unauthenticated attacker to crash the httpd workers. The highest threat from this liability is to service availability.	Story Points:	---
Clone Of:		Environment:
Last Closed:	2021-07-29 13:06:47 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	1986101
Bug Blocks:	1986104

Description Guilherme de Almeida Suckevicz 2021-07-26 17:07:24 UTC

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.

References:
https://github.com/zmartzone/mod_auth_openidc/security/advisories/GHSA-55r8-6w97-xxr4
https://github.com/zmartzone/mod_auth_openidc/releases/tag/v2.4.9

Upstream patch:
https://github.com/zmartzone/mod_auth_openidc/commit/dc672688dc1f2db7df8ad4abebc367116017a449

Comment 1 Guilherme de Almeida Suckevicz 2021-07-26 17:07:46 UTC

Created mod_auth_openidc tracking bugs for this issue:

Affects: fedora-all [bug 1986101]

Comment 2 Riccardo Schirone 2021-07-29 08:46:31 UTC

RHEL packages are compiled with `--without-hiredis`, which does not include the src/cache/redis.c file where this flaw lies. For this reason mod_auth_openidc as shipped in RHEL is not vulnerable to this flaw.

Comment 3 Product Security DevOps Team 2021-07-29 13:06:47 UTC

This bug is now closed. Further updates for individual products will be reflected on the CVE page(s):

https://access.redhat.com/security/cve/cve-2021-32785