CVE-2021-40438

CVE-2021-40438 is a critical-severity vulnerability in Apache Http Server with a CVSS 3.x base score of 9.0. It is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, confirming it has been exploited in the wild (added 2021-12-01). The underlying weakness is classified as CWE-918.

Key facts

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.

Frequently asked questions

What is 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 Server 2.4.48 and earlier.
How severe is CVE-2021-40438?
CVE-2021-40438 has a CVSS 3.x base score of 9.0, rated critical severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-40438 being actively exploited?
Yes. CVE-2021-40438 is on CISA's Known Exploited Vulnerabilities (KEV) catalog, added on 2021-12-01, which means active exploitation has been confirmed. It should be prioritised for remediation.
What products are affected by CVE-2021-40438?
CVE-2021-40438 primarily affects Apache Http Server. In total, 82 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-40438?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Because this CVE is known to be actively exploited, treat remediation as urgent — CISA KEV typically sets a short remediation deadline.
Does CVE-2021-40438 have an EU (EUVD) identifier?
Yes. CVE-2021-40438 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2021-27615. It is also flagged as exploited in the EUVD (since 2021-12-01).
When was CVE-2021-40438 published?
CVE-2021-40438 was published on 2021-09-16 and last updated on 2026-06-17.

References

Affected products (82)

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Other CWE-918 (Server-Side Request Forgery (SSRF)) vulnerabilities

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Threat intelligence

Threat-intel indicators referencing this CVE: