Page generated: 08 Nov 2026, 13:11 UTC
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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.

CVSS 9.0 (CRITICAL) KEV: KNOWN CATALOG

Attention and evidence

HYPE SCORE
0.0/10
REALITY · THREAT PRIORITY
8.8/10
General review priority; not probability

Evidence confidence: Exploitation recorded

Why this priority?
  • Recorded exploitation baseline: +7.00
  • Technical severity: CVSS 9: +1.35
  • Fresh EPSS: 100.00%: +0.50

General review priority, not probability, victim count or asset-specific risk. A range covers missing CVSS/EPSS inputs within the current evidence state.

Sources: 8 documents and public datasets.

Hype components

Headline sample (25%)
0/100
Press, 30 days (60%)
0/100
Grounded branding (15%)
0/100
HYPE TOTAL0/100

Sources and documents

Security Affairs
Press · 27 Dec 2021, 08:00 · Apache addressed a couple of severe vulnerabilities in Apache HTTP Server - Security Affairs
www.trendmicro.com
Press · 21 Dec 2021, 08:00 · How to detect Apache HTTP Server Exploitation - www.trendmicro.com
www.trendmicro.com
Press · 21 Dec 2021, 08:00 · How to detect Apache HTTP Server Exploitation - www.trendmicro.com
cyfirma
Press · 05 Dec 2021, 08:00 · Weekly Cyber Intelligence Trends & Advisory | Cyber Threat Actors - cyfirma
www.trendmicro.com
Press · 03 Dec 2021, 08:00 · Vulnerabilities Exploited for Monero Mining Malware Delivered via GitHub, Netlify - www.trendmicro.com
See all 8 source documents
www.trendmicro.com
Press · 03 Dec 2021, 08:00 · Vulnerabilities Exploited for Monero Mining Malware Delivered via GitHub, Netlify - www.trendmicro.com
Rapid7
Press · 30 Nov 2021, 08:00 · Active Exploitation of Apache HTTP Server CVE-2021-40438 - Rapid7
Check Point Research
Press · 18 Oct 2021, 07:00 · 18th October – Threat Intelligence Report - Check Point Research

Score evolution

● Hype   ● Reality

Earlier evidence-support scores are retained in history; this chart shows only the current priority definition.

First record: hype 0.0 · reality 8.8 (2026-11-02 15:12). The curve appears once the score changes.

Public exploit evidence

3

Public exploit entries / repo candidates

See 3 repos with metrics
RepositoryStarsForksLanguageUpdated
sixpacksecurity/CVE-2021-40438134Dockerfile24 Oct 2021, 10:21
ericmann/apache-cve-poc01Dockerfile11 Nov 2021, 19:53
n0m-d/CVE-2021-40438-POC00Python06 Dec 2025, 10:29
Evidence context and dated references

Reality is general threat/review priority, combining observed exploitation, CVSS severity and fresh EPSS. Evidence confidence is separate. This is not calibrated risk, a victim count or an asset-specific assessment. A range reflects missing numeric inputs.

Evidence in context

Confidence in exploitation evidence
Exploitation recorded
Priority basis
Recorded exploitation; CVSS 9; EPSS 100.0%
Attention, last 30 days
0 distinct story titles; 0 press documents; 0 publisher domains.
Technical potential
network access, no prior privileges, no user interaction, additional attack conditions.
Observed activity
Exploitation recorded in CISA KEV.
Known scale
Not quantified.
Evidence confidence basis
Trusted exploitation confirmation

Score evaluated: 2026-11-05 13:58:30.019134+00:00 · EPSS snapshot: 2026-11-05T12:03:04Z

Source event timeline
Published
16 Sep 2021, 14:40
First press mention
18 Oct 2021, 07:00
Added to the CISA KEV catalog
01 Dec 2021, 00:00
Latest press mention
27 Dec 2021, 08:00
Score calculated
05 Nov 2026, 13:58
PoCs on GitHub
3 repositories