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Fencer Vulns
medium 5.3

CVE-2021-32785 json

Format string bug in the Redis cache implementation

published 2021-07-22 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-19548

cvss
5.3
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
2.7%
EPSS 2.7% chance of exploitation in 30 days, percentile 86%
public exploits
0
none known

Summary

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.

Patch / fix

  • openidc mod_auth_openidc 2.4.9
  • libapache2-mod-auth-openidc Debian 14, Debian 13, Debian 12 2.4.9-1

debian advisories DEBIAN-CVE-2021-32785

  • apache2-mod_auth_openidc SLE Module for Server Applications 15 SP7, SLE Module for Server Applications 15 SP6, openSUSE Leap 15.6 2.4.17.1-150600.16.14.1
  • apache2-mod_auth_openidc SLES for SAP 12 SP5, SLES 12 SP5 2.4.0-3.23.1
  • apache2-mod_auth_openidc SLE Module for Server Applications 15 SP3, SLE Module for Server Applications 15 SP2 2.3.8-3.15.1

suse advisories SUSE-SU-2025:4532-1SUSE-SU-2021:3352-1SUSE-SU-2021:3020-1

  • apache2-mod_auth_openidc openSUSE Tumbleweed 2.4.9.4-1.2
  • apache2-mod_auth_openidc openSUSE Leap 15.2 2.3.8-lp152.5.6.1
  • apache2-mod_auth_openidc openSUSE Leap 15.3 2.3.8-3.15.1

opensuse advisories openSUSE-SU-2024:10624-1openSUSE-SU-2021:1277-1openSUSE-SU-2021:3020-1

  • httpd CBL-Mariner 2.0 2.4.52-1

azure linux advisories AZL-6479

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-32785 updated cvss 7.5

mod_auth_openidc: format string bug in the Redis cache implementation

  • Red Hat Enterprise Linux 7 mod_auth_openidc Red Hat Enterprise Linux 8 cjose, mod_auth_openidc Red Hat Enterprise Linux 9 mod_auth_openidc
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

2.73% chance of exploitation in the next 30 days, higher than 86% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 4.3 AV:N/AC:M/Au:N/C:N/I:N/A:P

Affected products

  • zmartzone mod_auth_openidc

Classification

Weakness
  • CWE-134 Use of Externally-Controlled Format String

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.