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Vulnerabilities

Vulnerability · CVE-2021-40438

Apache HTTP Server-Side Request Forgery (SSRF)

Published Sep 16, 2021 · catalog updated Aug 5, 2026 · Alpine Alpine Linux

Patch now

CVE-2021-40438 is in the CISA known-exploited catalog, due Dec 15, 2021. Confirm Alpine Alpine Linux against the vendor advisory and apply that fix. The CVSS score does not change the priority.

Severity
Critical9.0
Known exploitation
CISA KEV and VulnCheck KEV
EPSS
100.00%
Remediation
Remediation guidance
Affected products
alpine apache2 · cpe apache/http server · cpe fedoraproject/fedora · cpe redhat/enterprise linux · cpe redhat/enterprise linux eus · cpe redhat/enterprise linux for arm 64

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. Initial-access exploit intelligence.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • alpine apache22.4.49-r0
  • cpe apache/http serverversion unspecified
  • cpe fedoraproject/fedora34
  • cpe redhat/enterprise linux8.0
  • cpe redhat/enterprise linux eus8.1
  • cpe redhat/enterprise linux eus8.2
  • cpe redhat/enterprise linux eus8.4
  • cpe redhat/enterprise linux eus8.6
  • cpe redhat/enterprise linux eus8.8
  • cpe redhat/enterprise linux for arm 648.0
  • cpe redhat/jboss core services1.0
  • cpe redhat/software collections1.0
  • cpe resf/rocky linux8.0
  • vendor Apache Apacheversion unspecified

How to fix CVE-2021-40438

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

CVE-2021-40438 is in the CISA known-exploited catalog, due Dec 15, 2021. Confirm Alpine Alpine Linux against the vendor advisory and apply that fix. The CVSS score does not change the priority.

Which versions are affected?

Compare what you have installed with redhat/enterprise linux 8.0; redhat/enterprise linux eus 8.1; redhat/enterprise linux eus 8.2; redhat/enterprise linux eus 8.4. Apply updates per vendor instructions.

What should an analyst verify?

CWE-918: Server-Side Request Forgery (SSRF). EPSS 100.00%. The CISA KEV listing is the exploitation evidence. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Sep 16, 2021 · Catalog

    Detected

    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.

  2. Dec 1, 2021 · CISA KEV

    Known exploited

    Apply updates per vendor instructions.

  3. Dec 15, 2021 · CISA KEV

    Remediation due

    Apply updates per vendor instructions.

  4. Aug 5, 2026 · Catalog

    Updated

    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.

Sources

  • Alpine Linux SecurityPackage advisoryCVE-2021-40438

    CVE-2021-40438 is fixed in Alpine edge package apache2 2.4.49-r0 (main).

    security.alpinelinux.org
  • CISA KEVConfirmed exploitationCVE-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 Server 2.4.48 and earlier.

    cisa.gov
  • CVE.orgVulnerability recordCVE-2021-40438

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2021-40438

    30-day exploitation probability 100.0%

    first.org
  • NIST NVDVulnerability recordCVE-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 Server 2.4.48 and earlier.

    nvd.nist.gov
  • VulnCheck KEVConfirmed exploitationCVE-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 Server 2.4.48 and earlier.

    vulncheck.com

References

Freshness

Last verified in this catalog Oct 17, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.