CVE-2021-20718Network attack vector

Remote crash via missing Content-Type header

Published May 20, 2021 · Updated Aug 3, 2024

Denial-of-service in mod_auth_openidc 2.4.0 through 2.4.7 allows remote attackers to crash Apache via malformed POST requests. The module can crash when a POST request lacks a Content-Type header, as documented in the upstream 2.4.8.1 release notes. No authentication or user interaction is required, and the bounded consequence is interruption of Apache service rather than data disclosure or modification.

CVSS severity7.5
High
EPSS probability3.40%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial-of-service in mod_auth_openidc 2.4.0 through 2.4.7 allows remote attackers to crash Apache via malformed POST requests. The module can crash when a POST request lacks a Content-Type header, as documented in the upstream 2.4.8.1 release notes. No authentication or user interaction is required, and the bounded consequence is interruption of Apache service rather than data disclosure or modification.

The record

CVE
CVE-2021-20718
Published
May 20, 2021
Updated
Aug 3, 2024
Vendor
OpenIDC
Product
mod_auth_openidc
Classifications
CWE-400, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 20, 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=2.4.0 to 2.4.7

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

OpenIDC · mod_auth_openidcversion=2.4.0 to 2.4.7

Published CVSS scores

7.5NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.0NVDAV:N/AC:L/Au:N/C:N/I:N/A:P

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-400Uncontrolled Resource Consumption
T1499.004Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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