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.

CriticalCISA KEVRansomware

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

Senserva AI read on CVE-2021-40438CISA required actionOfficial fix for CVE-2021-40438Admin questions

Risk summary

CVSS base
9.0
EPSS exploit probability
100%
Severity
Critical
Added to KEV
2021-12-01
CISA due date
2021-12-15 (past due)
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 July 28, 2026. Data refreshed on every build from MSRC, CISA KEV, and FIRST EPSS.

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.

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.

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 twice a day (5 AM and 3 PM US Central).

More exploited Apache CVEs

The newest Apache entries on the CISA KEV catalog:

CVE-2026-34197CVE-2024-38475CVE-2025-24813CVE-2024-45195CVE-2024-27348CVE-2024-38856CVE-2024-32113CVE-2020-17519

All Apache exploited CVEs on one page: Apache vulnerabilities actively exploited.

Authoritative references

CVE recordNVD detailCISA KEV catalogFIRST.org EPSS

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

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Lexicon: the terms on this page
CVE
Common Vulnerabilities and Exposures. A unique ID for one publicly known vulnerability, such as CVE-2025-1234.
KB
Microsoft Knowledge Base article. The identifier for a specific Microsoft update.
KEV
CISA Known Exploited Vulnerabilities. CVEs confirmed exploited in the wild. Fix these first.
CVSS
Common Vulnerability Scoring System. A standardized Severity score from 0 to 10.
EPSS
Exploit Prediction Scoring System. The probability a CVE will be exploited in the next 30 days.
MSRC
Microsoft Security Response Center. Microsoft's Patch Tuesday advisories and KB-to-CVE mapping.
NVD
National Vulnerability Database (NIST). Authoritative CVE metadata and CVSS scores.
Ransomware
The vulnerability is linked to known ransomware activity.
Reference: Microsoft CVE and vulnerability management, the full CVE-to-patch lookup ranked by real-world risk, and the Microsoft patching guide, how Intune, Windows Autopatch, Defender, and Azure Update Manager fit together.
Data notice: this page, the feeds, and the API are provided as is, for informational purposes only, without warranty of any kind. Senserva, LLC does not guarantee the accuracy, completeness, or timeliness of third-party data (MSRC, NVD, CISA KEV, EPSS) and accepts no liability for actions taken based on it; verify against the authoritative vendor advisory before acting. Built daily with Senserva Trustworthy AI. All use of this data is subject to the Senserva EULA.