CVE-2021-32785Network attack vector

Apache worker crashes via double-interpolated Redis keys

Published Jul 22, 2021 · Updated Aug 3, 2024

Format string injection in OpenIDC mod_auth_openidc before 2.4.9 allows remote attackers to crash Apache workers through crafted cache keys. The Redis cache path formats each key into a command, then passes that completed string to hiredis as a format string for a second interpolation. Exploitation requires server-cache sessions with Redis and OIDCCacheEncrypt off; repeated requests interrupt service, with no demonstrated code execution.

CVSS severity5.3
Medium
EPSS probability2.73%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Format string injection in OpenIDC mod_auth_openidc before 2.4.9 allows remote attackers to crash Apache workers through crafted cache keys. The Redis cache path formats each key into a command, then passes that completed string to hiredis as a format string for a second interpolation. Exploitation requires server-cache sessions with Redis and OIDCCacheEncrypt off; repeated requests interrupt service, with no demonstrated code execution.

The record

CVE
CVE-2021-32785
Published
Jul 22, 2021
Updated
Aug 3, 2024
Vendor
OpenIDC
Product
mod_auth_openidc
Classifications
CWE-134, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 22, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 2.4.9

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

OpenIDC · mod_auth_openidcversion=< 2.4.9

Published CVSS scores

5.3GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-134Use of Externally-Controlled Format String
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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