Sigma rule: CVE-2021-41773 Exploitation Attempt

A detection rule from the SigmaHQ repository, shown as its author published it. Dataset version ref-bcffeec2b8e5, updated 2023-01-02T00:00:00.000Z.

Rule

Title
CVE-2021-41773 Exploitation Attempt
Status
test
Level
high
Author
daffainfo, Florian Roth
Date
2021-10-05
Modified
2023-01-02
File
rules-emerging-threats/2021/Exploits/CVE-2021-41773/web_cve_2021_41773_apache_path_traversal.yml
Commit
ccbb0369507f796db0b0ae6854c8a2be471b9d84

Detects exploitation of flaw in path normalization in Apache HTTP server 2.4.49.
An attacker could use a path traversal attack to map URLs to files outside the expected document root.
If files outside of the document root are not protected by "require all denied" these requests can succeed.
Additionally this flaw could leak the source of interpreted files like CGI scripts.
This issue is known to be exploited in the wild. This issue only affects Apache 2.4.49 and not earlier versions.

Log source

category
webserver

Detection

selection:
    cs-uri-query|contains:
        - '/cgi-bin/.%2e/'
        - '/icons/.%2e/'
        - '/cgi-bin/.%%32%65/'
        - '/icons/.%%32%65/'
        - '/cgi-bin/.%%%25%33'
        - '/icons/.%%%25%33'
    sc-status:
        - 200
        - 301
condition: selection

False positives (as the rule lists them)

  • Unknown

Tags

  • attack.initial-access
  • attack.t1190
  • cve.2021-41773
  • detection.emerging-threats

CVEs this rule names

MITRE ATT&CK ids this rule names

References

Read on 2026-11-03T00:58:21.399Z under licence sigma-drl-1.1@d5f4c36a from https://github.com/SigmaHQ/sigma/blob/ccbb0369507f796db0b0ae6854c8a2be471b9d84/rules-emerging-threats/2021/Exploits/CVE-2021-41773/web_cve_2021_41773_apache_path_traversal.yml

Sources and licences

  • SigmaHQ

    "CVE-2021-41773 Exploitation Attempt" by daffainfo, Florian Roth (SigmaHQ). Rule: https://github.com/SigmaHQ/sigma/blob/ccbb0369507f796db0b0ae6854c8a2be471b9d84/rules-emerging-threats/2021/Exploits/CVE-2021-41773/web_cve_2021_41773_apache_path_traversal.yml.
    Licensed under the Detection Rule License (DRL) 1.1: https://github.com/SigmaHQ/Detection-Rule-License

    Detection Rule License (DRL) 1.1

Cite this page

Dragons Eye Ransomware Tracker, "Sigma rule: CVE-2021-41773 Exploitation Attempt",
entity page, dataset version ref-bcffeec2b8e5, updated 2023-01-02T00:00:00.000Z,
https://ransomware-tracker.com/detections/sigma/3007fec6-e761-4319-91af-e32e20ac43f5 (accessed 2026-11-03).
Underlying source: SigmaHQ rule 3007fec6-e761-4319-91af-e32e20ac43f5, commit ccbb0369507f796db0b0ae6854c8a2be471b9d84.

Pages change. The dataset version identifies the data, but no archive of old versions is kept, so this citation cannot be replayed later.