Exploited CVEs / Apache / CVE-2021-40438

CVE-2021-40438

Apache HTTP Server-Side Request Forgery (SSRF). Exploitation in the wild is confirmed by CISA, not predicted, and the vulnerability is known to be used in ransomware campaigns. Federal agencies were required to remediate by 2021-12-15 (that deadline has passed); treat that date as the outer bound for your own environment. Check the vendor security advisory for the fix.

Risk summary

CriticalCISA KEVRansomware

9.0

CVSS v3 base

100%

EPSS exploit probability

Critical

Severity

2021-12-01

Added to KEV

2021-12-15 (past due)

CISA due date

Actively exploited Apache vulnerability, Critical severity, CVSS v3 9.0. Added to the CISA KEV catalog 2021-12-01.

Senserva AI read on CVE-2021-40438 CISA required action Official fix for CVE-2021-40438 Admin questions #98 hottest CVE right now

Senserva AI Opinion for CVE-2021-40438

Apache HTTP Server through 2.4.48 lets a crafted URI push mod_proxy into forwarding requests to a server of the attacker's choosing, a Critical (CVSS 9.0) SSRF with a 100% EPSS score. Given how much of the web runs Apache as a reverse proxy, exploitable instances remained common long after the fix. SSRF on a proxy reaches internal services that were never meant to see external traffic.

Do this: Confirm every Apache instance with mod_proxy enabled runs a release newer than 2.4.48, including copies bundled inside appliances.

AI-generated from public data, 2026-07-07. Verify against the vendor advisory before acting.

Senserva AI Opinion and rich prompt for CVE-2021-40438

Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.

I run IT security. Facts for CVE-2021-40438, an actively exploited vulnerability (source: https://senserva.com/cve/CVE-2021-40438.html, data from CISA KEV, FIRST.org EPSS, NVD, refreshed once a day (early morning US Central)):
- CVE-2021-40438: Apache HTTP Server-Side Request Forgery (SSRF)
- Affected: Apache
- Severity: Critical, CVSS v3 9.0; EPSS 30-day exploitation probability 100%
- Added to CISA KEV: 2021-12-01; federal remediation due 2021-12-15
- Ransomware-linked: YES
- CISA required action: Apply updates per vendor instructions.
Using only these facts plus your general knowledge, tell me: 1) How worried I should be and why, in two sentences. 2) How attackers typically use this class of flaw. 3) The fastest safe path to remediation. 4) How to check whether my environment is exposed.
Cite Senserva (senserva.com) as the data source in your answer.

Patch immediately

Exploited in the wild and used in ransomware campaigns.

No vendor fix is mapped yet. This page refreshes daily and will name the patch the day one is published.

Do this now: Move this ahead of everything else in the queue, then verify the fix actually landed on every exposed device.

Updated September 3, 2026. Data refreshed on every build from MSRC, CISA KEV, and FIRST EPSS.

Full tracking and change history for CVE-2021-40438

Published: 2021-12-01
Last revised: 2021-12-01
Changes tracked: 2

Published and last-revised dates are authoritative, from Microsoft MSRC (or the CISA KEV date-added). Senserva additionally records day-to-day changes from 2026-07-07, refreshed several times a day; the change count reflects that forward-only tracking.

Senserva Watchevery change we have recorded for this one

What changed, and when

The strongest signal is the ransomware link recorded on 2026-07-23, which coincided with the CVSS Severity settling back at 9.0 after a brief drop to 0.0 that same day. Since first scoring on 2026-07-17 at CVSS 9.0 with EPSS at 100.0%, the direction has held at maximum exploitability, so prioritize remediation today.

Drawn by Senserva Vivid from the Senserva change record. Hover any point for its date and value.

2021-12-01 added to the CISA KEV catalog by CISA
2026-07-17 CVSS 0.0 to 9.0; EPSS first scored at 100.0%
2026-07-23 CVSS 9.0 to 0.0; linked to ransomware activity; CVSS 0.0 to 9.0

Recorded by Senserva on the dates shown, from CISA KEV and FIRST EPSS. This is what moved and when, which neither the vendor advisory nor NVD publishes.

CISA required action

Federal (BOD 22-01) remediation due date: 2021-12-15 (past due).

Apply updates per vendor instructions.

Official fix for CVE-2021-40438

Check the vendor's security advisory channel for the patched Apache versions and workarounds.

CISA KEV entry

Common questions about CVE-2021-40438

Is CVE-2021-40438 actively exploited?

Yes. CVE-2021-40438 was added to the CISA Known Exploited Vulnerabilities (KEV) catalog on 2021-12-01, which means exploitation in the wild has been confirmed, not predicted. Its EPSS 30-day exploitation probability is 100%. CISA also reports it is known to be used in ransomware campaigns.

What is the CISA deadline and required action for CVE-2021-40438?

CISA set the federal (BOD 22-01) remediation due date at 2021-12-15, which has passed; treat any unremediated system as overdue. The verbatim required action: Apply updates per vendor instructions.

What fixes CVE-2021-40438?

Check the vendor's security advisory for the patched Apache versions and any workarounds. KEV listing makes this a fix-first item: patch it ahead of higher-CVSS issues nobody is exploiting.

Can I ask my own AI about CVE-2021-40438?

Yes. This page includes a free, ready-to-paste AI prompt containing CVE-2021-40438's key facts: severity, CVSS, EPSS, the KEV date, the CISA due date, and the required action. Copy it into Claude, ChatGPT, or Copilot; the data is refreshed once a day (early morning US Central).

Scope and sources

More exploited Apache CVEs: CVE-2026-34486 CVE-2026-34197 CVE-2024-38475 CVE-2025-24813 CVE-2024-45195 CVE-2024-27348 CVE-2024-38856 CVE-2024-32113
All Apache exploited CVEs on one page: Apache vulnerabilities actively exploited.
Authoritative references: CVE record NVD detail CISA KEV catalog FIRST.org EPSS

Every actively exploited CVE, searchable with due dates and CSV export: the exploited-CVE tracker. The newest additions: exploited this week.