Overview
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.
https://nvd.nist.gov/vuln/detail/CVE-2021-40438
Key Details
| Property | Value |
|---|---|
| CVE ID | CVE-2021-40438 |
| Vendor / Product | Apache — Apache |
| NVD Published | 2021-09-16 |
| NVD Last Modified | 2025-10-27 |
| CVSS 3.1 Score | 9 |
| CVSS 3.1 Vector | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H |
| Severity | CRITICAL |
| CWE | CWE-918 |
| CISA KEV Added | 2021-12-01 |
| CISA KEV Deadline | 2021-12-15 |
| Known Ransomware Use | No |
CVSS 3.1 Breakdown
Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High
Required Action
CISA BOD 22-01 Deadline: 2021-12-15.
Apply updates per vendor instructions.
Timeline
| Date | Event |
|---|---|
| 2021-12-01 | Added to CISA Known Exploited Vulnerabilities catalog |
| 2021-12-15 | CISA BOD 22-01 remediation deadline |
References
| Resource | Type |
|---|---|
| NVD — CVE-2021-40438 | Vulnerability Database |
| CISA KEV Catalog Entry | US Government |