CVE-2021-40438mod_proxy SSRF

A crafted request uri-path can cause mod_proxy to forward the request to an origin server choosen by the remote user. This issue affects Apache HTTP Server 2.4.48 and earlier.

9.0 CRITICALEPSS 99.99%⚡ Known Exploited (CISA KEV)NVD: Analyzed

Last updated: 2026-08-06 05:16 UTC

OverviewCVSS details

9.0CRITICALCVSS 3.1

Score source: NVD
NVD status: Analyzed
Published: Sep 16, 2021
Assigner: apache

Affected

Apache HTTP Server (Apache Software Foundation)

Versions: Apache HTTP Server 2.4 through 2.4.48

Exploitation

Public exploit: None listed
CISA KEV: Listed · Dec 1, 2021
KEV due date: Dec 15, 2021
Ransomware use: Known
SSVC: Exploitation active · Automatable yes · Impact total

EPSS · FIRST, scored Nov 7

99.99%chance of exploitation in 30 days

Higher than 99.99% of CVEs

CVSS 3.1 · NVD

9.0Critical

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

Attack vector: Network
Attack complexity: High
Privileges required: None
User interaction: None
Scope: Changed
Confidentiality impact: High
Integrity impact: High
Availability impact: High

CVSS 2.0 · NVD

6.8Medium

AV:N/AC:M/Au:N/C:P/I:P/A:P

Attack vector: Network
Attack complexity: Medium
Authentication: None
Confidentiality impact: Partial
Integrity impact: Partial
Availability impact: Partial

NVD status: Analyzed

Overview Affected Products References

NVD CVE.org

Overview

Severity

Score	Severity	Version	Vector String
9.0	CRITICAL	3.1NVD	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
6.8	MEDIUM	2.0NVD	AV:N/AC:M/Au:N/C:P/I:P/A:P

CISA required action

⚡ Known exploited · remediation due Dec 15, 2021

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Details

CVE ID: CVE-2021-40438
Status: Analyzed
Assigner (CNA): apache
Published: Sep 16, 2021
Last modified: 2026-08-06 05:16 UTC
Weaknesses: CWE-918 · Server Side Request Forgery (SSRF)

Sources

Refreshed hourly from the sources above. Last fetched 2026-11-08 11:23 UTC.