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Actively exploited in the wild. This CVE is on the CISA Known Exploited Vulnerabilities list — treat remediation as urgent. Federal remediation due by 17 Nov 2021. Known ransomware use
HTTP ServerWeb server / proxy · Apache

CVE-2021-42013

CRITICAL · 9.8 CVSS v3.1 Published 2021-10-07
Fix available
A fix is available. Upgrade to 9.2.6.0 / 18.1.0.1.0 or later.
See remediation →
100/100
Remediation priority · Urgent
In the wild Ransomware High EPSS Public exploit Remotely reachable No privileges Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
It was found that the fix for CVE-2021-41773 in Apache HTTP Server 2.4.50 was insufficient. An attacker could use a path traversal attack to map URLs to files outside the directories configured by Alias-like directives. If files outside of these directories are not protected by the usual default configuration "require all denied", these requests can succeed. If CGI scripts are also enabled for these aliased pathes, this could allow for remote code execution. This issue only affects Apache 2.4.49 and Apache 2.4.50 and not earlier versions.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Apache HTTP Server 2.4.50 contains an insufficient fix for CVE-2021-41773, allowing path traversal attacks to access files outside directories configured by Alias-like directives. If these files lack 'require all denied' protection and CGI scripts are enabled for aliased paths, remote code execution becomes possible.

MitigationUpgrade to Apache 2.4.51 or later. Ensure all directories outside Alias directives have 'require all denied' applied, and disable CGI scripts if not required.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
HTTP ServerWeb server / proxy
Affected:= 2.4.49= 2.4.50
FedoraOperating system
Affected:= 34= 35
Instantis EnterprisetrackApplication
Affected:= 17.1= 17.2= 17.3
Jd Edwards Enterpriseone ToolsApplication
Affected:< 9.2.6.0
Secure BackupApplication
Affected:< 18.1.0.1.0
Cloud BackupApplication
Affected:all versions

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed Apache HTTP Server version
    Run 'httpd -v' or 'apache2 -v' to obtain the server version number
    Affected if The version is exactly 2.4.49 or 2.4.50
  2. Verify CGI module is loaded
    Run 'httpd -M' or 'apache2ctl -M' and look for 'cgi_module' or 'cgid_module' in the loaded modules list
    Affected if CGI module is present and loaded
  3. Locate Alias or similar directory directives in configuration
    Search httpd.conf, apache2.conf, or included configuration files for 'Alias' directives and check which document root paths they define
    Affected if Alias directives map filesystem paths to URL paths without proper access controls
  4. Check if CGI is enabled on aliased paths
    Examine the <Directory> blocks in configuration files for aliased paths and verify if 'Options +ExecCGI' or 'Options FollowSymLinks' is set, and whether 'ScriptAlias' is used
    Affected if CGI execution is permitted on aliased paths without additional restrictions
  5. Verify access control restrictions on affected directories
    Look for 'Require all denied' directives within <Directory> blocks for the aliased paths; also check for 'AllowOverride None' settings that may prevent .htaccess overrides
    Affected if The aliased directories lack 'require all denied' statements or equivalent access restrictions

The environment is affected if running Apache HTTP Server version 2.4.49 or 2.4.50 with CGI enabled on Alias-mapped paths that do not have 'require all denied' protection, allowing path traversal to execute arbitrary CGI scripts outside the intended directory.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 9.2.6.0 / 18.1.0.1.0 or later
Fixed in 9.2.6.018.1.0.1.0
Vendor patch lists.apache.org →
Interim mitigation

Upgrade to Apache 2.4.51 or later. Ensure all directories outside Alias directives have 'require all denied' applied, and disable CGI scripts if not required.

Recommended fix High confidence

Apache HTTP Server 2.4.51 or later

  1. Identify the current Apache HTTP Server version using 'httpd -v' or 'apache2 -v'
  2. Download Apache HTTP Server 2.4.51 or later from the official Apache distribution (https://httpd.apache.org/)
  3. Backup the current Apache configuration and web content
  4. Install the upgraded Apache HTTP Server package
  5. Restart the Apache service using 'systemctl restart httpd' or 'apachectl restart'
  6. Verify the server is running and accessible
  7. Test that path traversal requests are now blocked (e.g., attempting /cgi-bin/%2e%2e/%2e%2e/%2e%2e/etc/passwd should return 403 Forbidden)
Caveat Standard Apache upgrade considerations apply; review release notes for any configuration changes between versions

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in HTTP Server Exploited in the wild — priority engagement
  • Consultation3.0 h
  • Implementation2.0 h
  • Testing3.0 h
  • Review / QA2.0 h
10.0 hours of engineering $1,770
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-42013 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data