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Vulnerability record · CVE-2021-32785 · published 22 July 2021

CVE-2021-32785: Mod auth openidc vulnerability

Openidc · Mod Auth Openidc

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.

7.5 CVSS 3.1 High EPSS 2.7% · top 14.5% CWE-134 · CWE-134
7.5CVSS 3.1 base score, v2 4.3
2.7%EPSS exploitation probability, 30 days
NoNot in CISA KEV
3Affected product versions listed by NVD
12References
17 Jun 2026Last modified by NVD

Description

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.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

3 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/zmartzone/mod_auth_openidc/commit/dc672688dc1f2db7df8ad4abebc367116017a449 PatchThird Party Advisory
https://github.com/zmartzone/mod_auth_openidc/releases/tag/v2.4.9 Release NotesThird Party Advisory
https://github.com/zmartzone/mod_auth_openidc/security/advisories/GHSA-55r8-6w97-xxr4 MitigationThird Party Advisory
https://lists.debian.org/debian-lts-announce/2023/04/msg00034.html Mailing ListThird Party Advisory
https://security.netapp.com/advisory/ntap-20210902-0001/ Third Party Advisory
https://www.oracle.com/security-alerts/cpuapr2022.html PatchThird Party Advisory
https://github.com/zmartzone/mod_auth_openidc/commit/dc672688dc1f2db7df8ad4abebc367116017a449 PatchThird Party Advisory
https://github.com/zmartzone/mod_auth_openidc/releases/tag/v2.4.9 Release NotesThird Party Advisory
https://github.com/zmartzone/mod_auth_openidc/security/advisories/GHSA-55r8-6w97-xxr4 MitigationThird Party Advisory
https://lists.debian.org/debian-lts-announce/2023/04/msg00034.html Mailing ListThird Party Advisory
https://security.netapp.com/advisory/ntap-20210902-0001/ Third Party Advisory
https://www.oracle.com/security-alerts/cpuapr2022.html PatchThird Party Advisory

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Source: NIST National Vulnerability Database (record CVE-2021-32785), CISA KEV, FIRST EPSS (scores of 2026-09-28). This page is refreshed as NVD updates the record.