CVE-2021-40438

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…

Browse: All 2021 CVEs · All vendors

CVSS score
9.0 Critical
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
CISA KEV
Yes — actively exploited (added 2021-12-01, remediation due 2021-12-15)
Ransomware
Known ransomware campaign use
Weakness (CWE)
CWE-918
Published
2021-09-16
Last modified
2026-08-06
NVD status
Analyzed

Description

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.

Affected products

Affected ranges per NVD CPE data; confirm exact versions in the vendor advisory.

Required action (CISA)

Apply updates per vendor instructions. Federal remediation deadline: 2021-12-15.

How to prioritize this

This vulnerability is on the CISA KEV list, meaning it is being actively exploited — treat it as urgent regardless of the raw CVSS number. Use the live CVE lookup for the latest NVD data, and the CVSS 3.1 calculator to model your own environmental score. For the actively exploited vulnerabilities that matter this week, read The Exploit HQ daily security brief.

References

FAQ

Is CVE-2021-40438 actively exploited?

Yes. CISA added CVE-2021-40438 to its Known Exploited Vulnerabilities (KEV) catalog on 2021-12-01, with a federal remediation deadline of 2021-12-15. A KEV listing means real-world exploitation is confirmed, so patching this should be prioritized above many higher-CVSS bugs that aren't being exploited.

What is the CVSS score of CVE-2021-40438?

CVE-2021-40438 has a CVSS base score of 9.0 (Critical). Its vector string is CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H.

Related vulnerabilities

Data source: NVD & CISA KEV. Shown as-is; nothing added. Last generated from NVD data — re-check the live tool for updates.