Vulnerability

CVE-2021-40438

Critical· 9.0KEVCVSS9EPSS94%

.rules3/5

Apache HTTP Server-Side Request Forgery (SSRF)

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.

Threat signal

100/100

Severe

Severity

critical

CVSS

9.0

EPSS

94%

Active

KEV

CISA KEV — actively exploited

1641d overdue

AffectedApache — Apache

Added to KEV

2021-12-01

Federal patch due (BOD 22-01)

2021-12-15

Required action (CISA verbatim)

Apply updates per vendor instructions.

Vendor advisory + references

https://nvd.nist.gov/vuln/detail/CVE-2021-40438

CISA 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.”

CVSS

v3.1Open in FIRST calculator →

9.0/ 10CRITICALCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

Attack VectorNetworkExploitable remotely over the internet — no local access needed.
Attack ComplexityHighRequires conditions outside attacker's control (race, brute-force, configuration
Privileges RequiredNoneUnauthenticated — no credentials needed.
User InteractionNoneFully automated — no victim action needed.
ScopeChangedImpact extends beyond the vulnerable component (e.g. sandbox escape).
Confidentiality ImpactHighTotal disclosure of sensitive data.
Integrity ImpactHighTotal compromise of integrity — full data modification possible.
Availability ImpactHighTotal loss of availability — full DoS possible.

EPSS

Exploit prediction · 30-day horizonFIRST.org →

94.4%

probability of exploitation in next 30 days

p100

higher than 100% of all CVEs

3-day trend↑ 0pp

Statistically about to be weaponized — top-tier triage urgency.

Vendor VEX

No VEX statements published for CVE-2021-40438. Vendors publish VEX (Vulnerability Exploitability eXchange) to assert per-product whether a CVE is actually exploitable in their distribution.

SSVCAct

Active exploitation with total impact on essential/support systems

exploitation: active
automatable: yes
impact: total
mission: support

Lifecycle

2021-10-15Vendor advisory · amazon-linuxALAS2-2021-1716 — ALAS2-2021-1716 (important): httpd
2021-12-01Added to CISA KEVransomware: Unknown
2021-12-01Published
2021-12-15Federal patch due (BOD 22-01)
2026-06-12Last modified1 source

Entity graph

2 nodes · 1 edges · click to pivot

CVEActorVendor advisoryIOCNews

Vendor advisories

amazon-linuxALAS2-2021-1716ALAS2-2021-1716 (important): httpd

No source-event history recorded yet. New revisions will appear here as ingestors re-fetch this CVE.