CVE-2021-42013Known exploitationNetwork attack vector

Remote file read via Alias path traversal

Published Oct 7, 2021 · Updated Oct 21, 2025

Path traversal in Apache HTTP Server 2.4.49 and 2.4.50 allows remote attackers to read files outside Alias-like directories via crafted URLs. The URL path normalizer permits encoded traversal sequences to escape an Alias-mapped directory, bypassing intended pathname restrictions. Access succeeds only when those outside directories lack the default require all denied protection; with CGI enabled for the aliased paths, the same condition allows remote code execution.

CVSS severity9.8
Critical
EPSS probability99.96%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Path traversal in Apache HTTP Server 2.4.49 and 2.4.50 allows remote attackers to read files outside Alias-like directories via crafted URLs. The URL path normalizer permits encoded traversal sequences to escape an Alias-mapped directory, bypassing intended pathname restrictions. Access succeeds only when those outside directories lack the default require all denied protection; with CGI enabled for the aliased paths, the same condition allows remote code execution.

The record

CVE
CVE-2021-42013
Published
Oct 7, 2021
Updated
Oct 21, 2025
Vendor
The Apache Software Foundation
Product
Apache HTTP Server
Classifications
CWE-22, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 7, 2021CVE publishedPublication date reported by the CVE source.
  2. Nov 3, 2021Exploitation reportedCISA Known Exploited Vulnerability catalog listing
  3. Oct 21, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=Apache HTTP Server 2.4.49
  2. Affected versionversion=Apache HTTP Server 2.4.50

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Apache Software Foundation · Apache HTTP Serverversion=Apache HTTP Server 2.4.49; version=Apache HTTP Server 2.4.50

Published CVSS scores

9.8NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsShadowserver observations through Sep 16, 2026. Gaps indicate unavailable data.
Sep 10, 2026Sep 16, 2026
View daily counts
Reporting dayUnique IPs
Sep 10, 2026Unavailable
Sep 11, 2026Unavailable
Sep 12, 2026Unavailable
Sep 13, 2026Unavailable
Sep 14, 2026180
Sep 15, 2026181
Sep 16, 2026169
Latest reporting daySep 16, 2026
Latest daily unique IPs169
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationReported
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-22Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Reported exploitation

Technologies

Your stack

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Your stack

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