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PatchSiren cyber security CVE debrief

CVE-2021-41773 Apache CVE debrief

CVE-2021-41773 is a path traversal vulnerability affecting Apache HTTP Server. CISA added it to the Known Exploited Vulnerabilities catalog on 2021-11-03 and marked it as known to be used in ransomware campaigns. For defenders, this is an urgent patching and verification item for any Apache HTTP Server deployment, especially exposed internet-facing instances.

Vendor
Apache
Product
HTTP Server
CVSS
Unknown
CISA KEV
Listed
Original CVE published
2021-11-03
Original CVE updated
2021-11-03
Advisory published
2021-11-03
Advisory updated
2021-11-03

Who should care

Apache HTTP Server administrators, platform and infrastructure teams, vulnerability management teams, SOC analysts, and any organization running web services backed by Apache HTTP Server.

Technical summary

The available corpus identifies the issue as a path traversal vulnerability in Apache HTTP Server. CISA’s KEV entry classifies it as a known exploited vulnerability and notes known ransomware campaign use. The provided official guidance is to apply updates per vendor instructions; no further technical details are supplied in the corpus.

Defensive priority

High. This is a CISA KEV-listed issue with known exploitation, so remediation should be prioritized ahead of routine patch cycles, especially for internet-facing Apache HTTP Server systems.

Recommended defensive actions

  • Identify all Apache HTTP Server installations and determine whether they are affected.
  • Apply vendor-recommended updates or mitigations as soon as possible.
  • Prioritize external-facing and business-critical servers for remediation.
  • Validate that patching completed successfully and that the updated version is in place.
  • Review web server access logs and related monitoring for unusual requests or suspicious activity around the exposure window.

Evidence notes

Evidence is limited to the supplied official metadata: CVE published/modified on 2021-11-03; CISA KEV added on 2021-11-03 with due date 2021-11-17; known ransomware campaign use is marked as Known; the KEV notes point to the NVD entry for CVE-2021-41773.

Official resources

CVE published and modified: 2021-11-03. CISA KEV date added: 2021-11-03. CISA due date: 2021-11-17. Known ransomware campaign use: Known.