CVE-2021-32785

Published: 22 July 2021

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.

Priority

Cvss 3 Severity Score

7.5

Score breakdown

Status

Package	Release	Status
libapache2-mod-auth-openidc Launchpad, Ubuntu, Debian	bionic	Needed
	focal	Needed
	hirsute	Ignored (end of life)
	impish	Not vulnerable (2.4.9-1)
	jammy	Not vulnerable (2.4.9-1)
	kinetic	Not vulnerable (2.4.9-1)
	lunar	Not vulnerable (2.4.9-1)
	mantic	Not vulnerable (2.4.9-1)
	noble	Not vulnerable (2.4.9-1)
	trusty	Does not exist
	upstream	Released (2.4.9-1)
	xenial	Needs triage

Severity score breakdown

Parameter	Value
Base score	7.5
Attack vector	Network
Attack complexity	Low
Privileges required	None
User interaction	None
Scope	Unchanged
Confidentiality	None
Integrity impact	None
Availability impact	High
Vector	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

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