What is CVE-2021-32785?

CVE-2021-32785 is a medium-severity vulnerability in Apache Http Server, classified under Use of Externally-Controlled Format String. CVSS score: 5.3/10. Published 2021-07-22.

How severe is CVE-2021-32785?

Medium severity. CVSS v3 base score is 5.3 out of 10.

Is CVE-2021-32785 known to be exploited?

1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Vulnerability in Apache Http Server

CVE-2021-32785

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.

EPSS: 0.027 (84.6th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L.

Affected products

Apache Http_server
Netapp Cloud_backup
Openidc Mod_auth_openidc
Zmartzone Mod_auth_openidc — versions < 2.4.9
Debian Debian_linux — versions 10.0

Weakness classification (CWE)

CWE-134 — Use of Externally-Controlled Format String

Public proof-of-concept exploits

ARPSyndicate/cve-scores

References

security-advisories@github.com (Third Party Advisory, Mitigation)
security-advisories@github.com (Patch, Third Party Advisory)
security-advisories@github.com (Third Party Advisory, Release Notes)
security-advisories@github.com (Patch, Third Party Advisory)
security-advisories@github.com (Third Party Advisory)
security-advisories@github.com (mailing-list, Mailing List, Third Party Advisory)

Frequently asked questions

What is CVE-2021-32785?: CVE-2021-32785 is a medium-severity vulnerability in Apache Http Server, classified under Use of Externally-Controlled Format String. CVSS score: 5.3/10. Published 2021-07-22.
How severe is CVE-2021-32785?: Medium severity. CVSS v3 base score is 5.3 out of 10.
Is CVE-2021-32785 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.