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CVE-2021-40438

mod_proxy SSRF

CRITICAL
9
CVSS Score
Published: September 16, 2021 at 02:40 PM UTC
Updated: August 6, 2026 at 05:16 AM UTC
40 products affected across 11 vendorsDebian LinuxFedoraEnterprise Linux

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Severity
CRITICAL9
Exploitation
CISA KEV
Exploit prediction
EPSS 100%
SSVC
Active

Actively Exploited

CISA Known Exploited Vulnerabilities (KEV) Catalog

EPSS Score100.0%

EPSS (Exploit Prediction Scoring System) estimates a 100.0% chance this CVE is exploited in the wild within the next 30 days — higher than 100% of all CVEs. It complements CVSS: a high EPSS on a mid-severity CVE can still be urgent.

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.

Required Action
Apply updates per vendor instructions.
Ransomware Use
Known
Added to KEV
Dec 1, 2021
Remediation Due
Dec 15, 2021
1782 days overdue
Notes
https://nvd.nist.gov/vuln/detail/CVE-2021-40438

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

References (20)

x_refsource_CONFIRMThird Party Advisory
Source: [email protected]
https://cert-portal.siemens.com/productcert/pdf/ssa-685781.pdf
x_refsource_MISCRelease NotesVendor Advisory
Source: [email protected]
https://httpd.apache.org/security/vulnerabilities_24.html
Mailing Listx_refsource_MLIST
Source: [email protected]
https://lists.apache.org/thread.html/r210807d0bb55f4aa6fbe1512be6bcc4dacd64e84940429fba329967a%40%3Cusers.httpd.apache.org%3E
Mailing Listx_refsource_MLIST
Source: [email protected]
https://lists.apache.org/thread.html/r2eb200ac1340f69aa22af61ab34780c531d110437910cb9c0ece3b37%40%3Cbugs.httpd.apache.org%3E
Mailing Listx_refsource_MLIST
Source: [email protected]
https://lists.apache.org/thread.html/r3925e167d5eb1c75def3750c155d753064e1d34a143028bb32910432%40%3Cusers.httpd.apache.org%3E
Mailing Listx_refsource_MLIST
Source: [email protected]
https://lists.apache.org/thread.html/r61fdbfc26ab170f4e6492ef3bd5197c20b862ce156e9d5a54d4b899c%40%3Cusers.httpd.apache.org%3E
Mailing Listx_refsource_MLIST
Source: [email protected]
https://lists.apache.org/thread.html/r82838efc5fa6fc4c73986399c9b71573589f78b31846aff5bd9b1697%40%3Cusers.httpd.apache.org%3E
Mailing Listx_refsource_MLIST
Source: [email protected]
https://lists.apache.org/thread.html/r82c077663f9759c7df5a6656f925b3ee4f55fcd33c889ba7cd687029%40%3Cusers.httpd.apache.org%3E

SSVC — Action Prioritization

SSVCActiveAutomatableTotal impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

9CRITICALCISA-ADP
Attack Vector
NETWORK
Complexity
HIGH
Privileges
NONE
User Interaction
NONE
Scope
CHANGED
Confidentiality
HIGH
Integrity
HIGH
Availability
HIGH
Vector?

Quick Info

StatusANALYZED
CWE
CWE-918

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