CVE-2021-40438

CRITICALNVD 9.09.0—Trending — 5 sources updated this weekExploited in the wild

9.0

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.

CVSS v3: 9.0
EG Score: 9.0(high)
EPSS: 100.0%
KEV: ⚠ Exploited

Published

September 16, 2021

Last Modified

October 27, 2025

Advisory Details (9)

Auto-updated Jun 2, 2026

⚠️ Active exploitation confirmed. Patch available.

generic Patch Available

[SECURITY] [DLA 2776-1] apache2 security update

https://lists.debian.org/debian-lts-announce/2021/10/msg00001.html

generic

https://lists.apache.org/thread.html/rf6954e60b1c8e480678ce3d02f61b8a788997785652e9557a3265c00%40%3Cusers.httpd.apache.org%3E

generic

https://lists.apache.org/thread.html/r82c077663f9759c7df5a6656f925b3ee4f55fcd33c889ba7cd687029%40%3Cusers.httpd.apache.org%3E

generic

https://lists.apache.org/thread.html/r82838efc5fa6fc4c73986399c9b71573589f78b31846aff5bd9b1697%40%3Cusers.httpd.apache.org%3E

generic

https://lists.apache.org/thread.html/r61fdbfc26ab170f4e6492ef3bd5197c20b862ce156e9d5a54d4b899c%40%3Cusers.httpd.apache.org%3E

generic

https://lists.apache.org/thread.html/r3925e167d5eb1c75def3750c155d753064e1d34a143028bb32910432%40%3Cusers.httpd.apache.org%3E

generic

https://lists.apache.org/thread.html/r2eb200ac1340f69aa22af61ab34780c531d110437910cb9c0ece3b37%40%3Cbugs.httpd.apache.org%3E

generic

https://lists.apache.org/thread.html/r210807d0bb55f4aa6fbe1512be6bcc4dacd64e84940429fba329967a%40%3Cusers.httpd.apache.org%3E

generic Patch Available🔴 Active Exploitation

Apache HTTP Server 2.4 vulnerabilities - The Apache HTTP Server Project

https://httpd.apache.org/security/vulnerabilities_24.html

Patch Availability(9)

Vendor / Ecosystem	Fixed in / Patch	Released	Source
ubuntu	apache2-bin (2.4.29-1ubuntu4.17) @ bionic	2026-06-04	ubuntu
ubuntu	apache2-utils (2.4.18-2ubuntu3.17+esm2) @ xenial	2026-06-04	ubuntu
redhat	httpd-0:2.4.6-90.el7_7.1	2021-10-14	redhat
redhat	httpd:2.4-8010020211008125020.c27ad7f8	2021-10-13	redhat
redhat	httpd:2.4-8020020211008164029.4cda2c84	2021-10-13	redhat
redhat	httpd:2.4-8040020211008164252.522a0ee4	2021-10-12	redhat
redhat	httpd24-httpd-0:2.4.34-22.el7.1	2021-10-11	redhat
redhat	patch	2021-10-07	redhat
redhat	jbcs-httpd24-mod_security-0:2.9.2-65.GA.jbcs.el7	2021-10-07	redhat

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

CWE-918Server-Side Request Forgery (SSRF)

All Vendor Advisories

(10)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 20× in last 7d / 20× in last 30d)

Every time one of our enrichment pipelines (NVD, MITRE cvelistV5, EPSS, CISA KEV, GHSA, OSV, vendor advisories) ran against this CVE. Most recent first.

2026-06-04 05:56 UTCEG score recompute
2026-06-04 05:56 UTCVendor advisory
2026-06-04 05:56 UTCGHSA enrichment
2026-06-04 01:50 UTCEG score recompute
2026-06-04 01:50 UTCVendor advisory
2026-06-04 01:50 UTCGHSA enrichment
2026-06-03 21:44 UTCEG score recompute
2026-06-03 21:44 UTCVendor advisory
2026-06-03 21:44 UTCGHSA enrichment
2026-06-03 19:09 UTCkev_newly_listed
2026-06-03 17:38 UTCEG score recompute
2026-06-03 17:38 UTCVendor advisory
2026-06-03 17:38 UTCGHSA enrichment
2026-06-03 13:30 UTCEG score recompute
2026-06-03 13:30 UTCVendor advisory
2026-06-03 13:30 UTCGHSA enrichment
2026-06-03 09:24 UTCEG score recompute
2026-06-03 09:24 UTCVendor advisory
2026-06-03 09:24 UTCGHSA enrichment
2026-06-03 05:17 UTCEG score recompute

Publicly available exploits

(5 references)

Working exploit code is in the public domain (4 GitHub PoCs). Defenders should treat patch urgency accordingly — public PoCs typically lead to mass-exploitation within 24-72 hours.

GitHub PoCsergiovks/CVE-2021-40438-Apache-2.4.48-SSRF-exploit
First seen Dec 12, 2023
CVE-2021-40438 Apache <= 2.4.48 SSRF exploit
Open source ↗
GitHub PoCBabyTeam1024/CVE-2021-40438
First seen Oct 28, 2021
Open source ↗
GitHub PoCsixpacksecurity/CVE-2021-40438
First seen Oct 24, 2021
CVE-2021-40438 exploit PoC with Docker setup.
Open source ↗
GitHub PoCxiaojiangxl/CVE-2021-40438
First seen Oct 18, 2021
Open source ↗
Nucleihttp/cves/2021/CVE-2021-40438.yaml
First seen Jan 1, 2021
Apache <= 2.4.48 Mod_Proxy - Server-Side Request Forgery
Open source ↗

Frequently asked(6)

What is CVE-2021-40438?

CVE-2021-40438 is a critical vulnerability published on September 16, 2021. 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.

When was CVE-2021-40438 disclosed?

CVE-2021-40438 was first published in the National Vulnerability Database on September 16, 2021, with the most recent update on October 27, 2025. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.

Is CVE-2021-40438 actively exploited?

Yes. CISA added CVE-2021-40438 to the Known Exploited Vulnerabilities catalog on December 1, 2021, affecting Apache Apache. KEV listing indicates confirmed exploitation in the wild; this CVE warrants immediate patching attention.

What is the CVSS score of CVE-2021-40438?

CVE-2021-40438 has a CVSS v3 base score of 9.0 (NVD).

Which products are affected by CVE-2021-40438?

CVE-2021-40438 affects Apache Apache. The full affected-products list, including version ranges and fixed versions, is shown in the Affected Packages section of this page.

How do I remediate CVE-2021-40438?

Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-40438, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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CVE-2021-40438

Published

Last Modified

Advisory Details (9)

[SECURITY] [DLA 2776-1] apache2 security update

Apache HTTP Server 2.4 vulnerabilities - The Apache HTTP Server Project

Patch Availability(9)

Weakness Classification(1)

All Vendor Advisories

Data Freshness Timeline

Publicly available exploits

Frequently asked(6)

Dependency Blast Radius

Is Your Infrastructure Affected by CVE-2021-40438?

Same vendor

Same CWE

CVE-2021-40438

📅 Published

🔄 Last Modified

📋 Advisory Details (9)

[SECURITY] [DLA 2776-1] apache2 security update

Apache HTTP Server 2.4 vulnerabilities - The Apache HTTP Server Project

Patch Availability(9)

Weakness Classification(1)

All Vendor Advisories

Data Freshness Timeline

Publicly available exploits

❓ Frequently asked(6)

Dependency Blast Radius

Is Your Infrastructure Affected by CVE-2021-40438?

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Advisory Details (9)

Frequently asked(6)

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