CVE-2021-41773 remediation guide

Apache HTTP Server

A flaw was found in a change made to path normalization in Apache HTTP Server 2.4.49. 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 is known to be exploited in the wild. This issue only affects Apache 2.4.49 and not earlier versions. The fix in Apache HTTP Serv...

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Research in progress

A verified fixed-version field is not available. Use the linked NVD and supporting references, then confirm the vendor-supported path before changing production systems.

ProductApache HTTP Server

Affected versionsApache HTTP Server 2.4 2.4.49, 2.4.49, 34, 35, 17.1, 17.2, 17.3

Fixed versionsNo verified fixed-version field is available yet

Priority basisImmediate · CVSS 9.8 · EPSS 100.0%

Identify the affected asset

Confirm whether Apache HTTP Server is installed, record the deployed version and installation path, and identify exposed interfaces.

Record the product name, package or appliance identifier, and installed version.
Identify internet-facing, administrative, API, and internal access paths.
Preserve the pre-change configuration and relevant service logs.

Validate the affected-version match

Compare the deployed version with the affected range: Apache HTTP Server 2.4 2.4.49, 2.4.49, 34, 35, 17.1, 17.2, 17.3. Treat incomplete inventory results as unresolved.

Prioritize with independent signals

CISA has listed this vulnerability in the Known Exploited Vulnerabilities catalog. Combine this signal with asset criticality, exposure, compensating controls, and business impact.

Apply supported remediation

Apply updates per vendor instructions.

Verify the result

Confirm the resulting version, service health, authentication and access paths, monitoring coverage, and relevant security logs.

Confirm the expected version and package state.
Run a functional health check for critical service paths.
Review authentication, error, application, and security monitoring logs.
Reassess exposure if the supported fix cannot be applied.

Operational boundary

This page does not replace the vendor advisory, support contract, change-management process, or recovery plan. Do not infer that an asset is unaffected from an incomplete inventory query or a missing fixed-version field.