VulnTideExploited vulnerabilities, by vendor. Data as of .
Known exploitedIn CISA's KEV catalog since Ransomware use: known
Apache Apache

CVE-2021-40438: Apache HTTP Server-Side Request Forgery (SSRF)

Is it exploited?

Yes. CISA added it to the Known Exploited Vulnerabilities catalog on , 76 days after the CVE record was published.

How likely is exploitation in the next 30 days?
100%

EPSS score, percentile 100 of all scored records

How severe?
9.0 Critical

CVSS v3.1 base score, from CISA's enrichment of the record

What should I do?

CISA deadline . Apply updates per vendor instructions.

Advisories and patches (5)

Which versions are affected?

Affected

  • Apache HTTP Server 2.4 through 2.4.48

Versions by product

Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of ; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of ; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of . About the data.

What to do

Required action, set by CISA

Apply updates per vendor instructions.

CISA due date for this action: .

Advisories and patches

Linked from CISA's catalog entry

Affected products and versions

As listed in the CVE record.

Apache Software Foundation Apache HTTP Server
StatusVersions
AffectedApache HTTP Server 2.4 through 2.4.48

Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of . About the data.

About this vulnerability

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.

Summary: CISA's KEV catalog, as of .

  • CISA added CVE-2021-40438 to its Known Exploited Vulnerabilities (KEV) catalog on 1 Dec 2021.
  • CISA marks it as known to be used in ransomware campaigns.
  • The due date CISA sets for the required action is 15 Dec 2021.
  • The CVE record was published on 16 Sep 2021, 76 days before it was added to KEV.
  • The CVE record carries a CVSS v3.1 base score of 9.0 (Critical), taken from CISA's enrichment of the record.
  • FIRST's EPSS model puts the probability of exploitation in the next 30 days at 100% (percentile 100), as of 28 Oct 2026.
  • CISA's SSVC assessment in the CVE record: exploitation active, automatable yes, technical impact total.

Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of ; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of ; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of . About the data.

Description

mod_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.

Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of . About the data.

Weakness

  • CWE-918: Server Side Request Forgery (SSRF)

CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record and the KEV entry.

Timeline

DateEvent
CVE record published
Added to CISA KEV
CISA due date for the required action
CVE record last updated

References

7 more in the CVE record.

More exploited Apache vulnerabilities

  • CVE-2016-3081: Apache Struts Command Injection Vulnerability (added )
  • CVE-2026-34486: Apache Tomcat Missing Encryption of Sensitive Data Vulnerability (added )
  • CVE-2026-34197: Apache ActiveMQ Improper Input Validation Vulnerability (added )
  • CVE-2024-38475: Apache HTTP Server Improper Escaping of Output Vulnerability (added )
  • CVE-2025-24813: Apache Tomcat Path Equivalence Vulnerability (added )
  • CVE-2024-45195: Apache OFBiz Forced Browsing Vulnerability (added )