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CVE-2021-40438

mod_proxy SSRF

  • Critical 9.0
  • Exploited: added to CISA KEV 1 Dec 2021
  • Used in ransomware campaigns

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.

Key facts

Published
16 Sep 2021
Last changed
6 Aug 2026
Assigned by
apache
KEV added
1 Dec 2021
KEV fix due
15 Dec 2021
Used in ransomware
Yes, according to CISA
EPSS
99.999% likely to be exploited in the next 30 days, higher than 99.997% of CVEs (scores for 15 Nov 2026)
SSVC (CISA)
Exploitation: active; Automatable: yes; Technical impact: total

Severity scores

Each score is shown as its source gave it. They are not averaged or merged.

  • 9.0CVSS 3.1, Criticalfrom CISA (ADP container)CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

What to do

  • Apply updates per vendor instructions.CISA KEV required action

Historical context and remediation

This reference retains the original CVE publication date. A recent record update does not mean a new attack occurred.

No separately sourced impact summary is available on this page yet. Consult the description, version data and dated exploitation evidence.

Version statuses below come from the CNA. An “unaffected” version is not necessarily a currently supported release or proof of a patch date. EPSS is a dated risk estimate, not a count of historical attacks.

Read the original CVE record.

Affected products

VendorProductVersions
Apache Software FoundationApache HTTP Server
  • Apache HTTP Server 2.4 up to and including 2.4.48 (affected)

Timeline

  1. 16 Sep 2021 2.4.49 released
  2. 16 Sep 2021 Published
  3. 1 Dec 2021 Added to the CISA KEV catalogue

Weakness

Practice this bug class

HackZoneLabs has a hands-on lab on SSRF (CWE-918).

Open the learning platform

References