Vulnerability report

Active exploitation observed Confirmed confidence In CISA KEV

CVE-2021-41773

Apache HTTP Server Path Traversal

Apache HTTP Server · Apache HTTP Server 2.4 2.4.49

Watch CVE-2021-41773 Browse KEV feed
Severity
CVSS 7.5 · High
Confidence
Confirmed
Exploit status
Observed in sensors
EPSS
100.0%
First observed
10 Jun 2026
Last observed
09 Oct 2026

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2021-41773 is an unauthenticated vulnerability affecting 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...

Is it exploited?

Yes. Previdian sensors observed exploitation attempts with confirmed confidence. Listed in CISA KEV.

Who is affected?

Apache HTTP Server apache http server 2.4 2.4.49.

What should we do?

Patch immediately, validate internet-facing exposure, and monitor for matching requests.

Overview

A flaw was found in a change made to path normalization in Apache HTTP Server 2.4.49

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 Server 2.4.50 was found to be incomplete, see CVE-2021-42013.

Apache Software Foundation Affected
Apache HTTP Server
Apache HTTP Server 2.4 2.4.49
View vendor advisory (opens in new tab)
Published
05 Oct 2021
Exploitation Reported
03 Nov 2021
Attack vector
Remote
Complexity
Low
Privileges
None
User interaction
None

Tags

metasploit ransomware cisa apache malware nuclei_scanner

CVE References

Exploitation evidence

Why Previdian marks this CVE as exploited

Third-party attestation and first-party sensor observation are shown separately so teams can judge the evidence chain.

Exploited in the wild

CISA

Recorded 03 Nov 2021

A trusted third party reported exploitation.

Active exploitation observed

Previdian sensor

First observed 09 Jul 2026

Previdian first observed exploitation attempts targeting this vulnerability in our honeypot sensors.

Used in malware

CISA

Recorded 03 Nov 2021

Malware families have been linked to exploitation of this CVE.

Proof of concept available

GitHub

Recorded 05 Oct 2021

Public scanner or PoC coverage increases practical exploitability.

Known exploited vulnerability sources

Per-source evidence links for KEV attestations are available through the Previdian Pro API.

Learn about Pro API access
Source Added
CISA First 2021-11-03 00:00 UTC
Previdian Sensors 2026-07-16 15:07 UTC

Operational indicators for this CVE are listed under Detection.

Sensor telemetry

First-party evidence of exploitation activity

Previdian sensors recorded exploitation attempts targeting this vulnerability. The cards and chart show volume, unique attackers, and daily activity.

12,780

Attempts observed

1,773

Unique attacker IPs

82

Attacker countries

AE · AM · AR · AT · AU · BD · BE · BG · BR · CA · CH · CI · CL · CM · CN · CO · CZ · DE · DK · DO · DZ · EE · ER · ES · ET · FI · FR · GB · GE · GR · GT · HK · HU · ID · IE · IL · IN · IQ · IR · IS · IT · JP · KR · KZ · LK · LT · LU · LV · LY · MA · MW · MX · MY · MZ · NG · NL · NP · NZ · PA · PE · PH · PK · PL · PT · PY · RS · RU · SA · SC · SE · SG · SO · TH · TR · TW · UA · US · UZ · VN · YE · ZA · ZM

81

Sensors observed

CVE-2021-41773 exploitation attempts over the last 91 days

Daily events observed by Previdian sensors

Updated 09 Oct 2026

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249
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11 Jul 30 Jul 18 Aug 6 Sep 9 Oct

First observed 10 Jun 2026 · Last observed 09 Oct 2026

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Detection

Operational artifacts and observed signals

Make the evidence actionable in scanner, SOC, and edge-control workflows.

Observed signals

Request targets
User-Agents
Callback hosts
18
66
8

Request targets and User-Agents available in Pro. Callback host details available in Enterprise.

Virtual patch status

Previdian virtual patch guidance is available for this CVE.

AWS WAF Cloudflare ModSecurity

Attacker IP Indicators

Attacker IP indicators observed · available in Pro and Enterprise.

Sensor-derived attacker IP indicators are available to Pro and Enterprise accounts under Detection and through the Pro API.

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Scanner Artifacts

Scanner and exploit-framework references linked to this CVE.

Scanner Reference Detected
Metasploit https://github.com/rapid7/metasploit-framework/blob/master/modules/exploits/multi/http/apache_normalize_path_rce.rb 28 Apr 2025
Nuclei https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2021/CVE-2021-41773.yaml 25 Apr 2025

Virtual Patch Detail

Compensating WAF rules for this CVE.

Available

Enterprise feature. Virtual patch rule content and deployable vendor exports (ModSecurity, Cloudflare, AWS WAF) are available to Previdian Enterprise users.

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Risk and context

Severity, weaknesses, and research context

CVSS v3.1

7.5 High

Potential damage if exploited. Separate from whether attackers are using it.

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

EPSS

100.0%

Estimated chance of exploitation in the next 30 days. Previdian's warning comes from evidence, not this score.

Weaknesses

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

Potential Proof of Concepts

These PoCs are unverified and could contain malware. Use at your own risk.

thehackersbrain/CVE-2021-41773

github · Created 2022-03-12 21:24:55 UTC · 107 stars · AI assessment 90%

Apache2 2.4.49 - LFI & RCE Exploit - CVE-2021-41773

blasty/CVE-2021-41773

github · Created 2021-10-06 07:17:05 UTC · 208 stars · AI assessment 90%

CVE-2021-41773 playground

Ls4ss/CVE-2021-41773_CVE-2021-42013

github · Created 2021-10-06 02:28:41 UTC · 21 stars · AI assessment 90%

Apache HTTP Server 2.4.49, 2.4.50 - Path Traversal & RCE

lorddemon/CVE-2021-41773-PoC

github · Created 2021-10-05 23:53:48 UTC · 37 stars · AI assessment 90%

iilegacyyii/PoC-CVE-2021-41773

github · Created 2021-10-05 17:30:43 UTC · 47 stars · AI assessment 90%

Apache 2.4.49 - Path Traversal and Remote Code Execution

nuclei · Created Unknown

Timeline

From disclosure to observed exploitation

  1. 13:00 UTC

    Virtual patch available

    Compensating WAF rule available to block exploitation

  2. 15:16 UTC

    Observed by Previdian sensors

    Evidence-backed exploitation signal

  3. 18:51 UTC

    Indicators of compromise added (2126)

    Indicators of compromise recorded

  4. 15:02 UTC

    Metasploit module available

    Exploit module available

  5. 00:00 UTC

    Nuclei template available

    Scanner coverage available

  6. 00:00 UTC

    Added to CISA KEV

    Listed in the CISA Known Exploited Vulnerabilities catalog

  7. 00:00 UTC

    First public exploitation report

    Exploit observed in malware

  8. 17:30 UTC

    Public PoC available

    Public proof-of-concept code published

  9. 08:40 UTC

    CVE published

    Vulnerability disclosed publicly

  10. 00:00 UTC

    CVE ID reserved

    Identifier reserved by the CNA

Pro API

Automate this intelligence

Confidence, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.

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  • Evidence confidence and provenance
  • First-party sensor telemetry
  • PoC and scanner references
  • Affected versions and enrichment
  • Automation-ready JSON delivery

GET /api/v2/pro/kevs/CVE-2021-41773

Free JSON includes basic KEV fields 
{
  "cve_id": "CVE-2021-41773",
  "confidence": "Confirmed",
  "cvss_score": 7.5,
  "cvss_estimated": false,
  "epss_score": 0.99992,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": true
  },
  "sensor_telemetry": { "attempts": 12780, "sensors": 81 }
}