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CVE-2021-41773

Apache — Apache HTTP Server Path Traversal Vulnerability

Apache · CWE-22 — Path traversal · in CISA KEV since 2021-11-03

ExigentKEV since 2021 · listed over a yearRansomwareCISA KEVActively Exploited
94

EVRS 94 of 100 Immediate

Out-of-Band / Urgent Remediation

Rank 32 of 2,955 tracked

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Why it scores 94

Evidence available: 6 of 7 signals

Listed in the CISA KEV catalog, and associated with known ransomware campaigns.

  • CISA KEVApplied
  • RansomwareApplied
  • Vendor exploitationDid not apply
  • EPSSApplied
  • Microsoft Exploitability IndexNot applicable
  • Pre-patch disclosureNo data
  • KEV recencyDid not apply
  • CVSSApplied

The band answers “how soon”, not “how bad”. No data for: Pre-patch disclosure. Why some signals show no data

Fix

Patch or fixed version identified

CISA required action

Fixed in

apache2 -> 2.4.50-1

Affected versions

  • http server2.4.49
  • instantis enterprisetrack17.117.217.3
  • cloud backup
  • fedora3435

Remediation

Apply updates per vendor instructions.

Fixed versions from NVD.

Evidence

Each value with its source
MeasureValueSource
CVSS base scoreHow severe the flaw is in itself. It does not say how likely an attack is. 9.8 NVD
FIRST EPSSFIRST's estimate of the chance this is exploited in the next 30 days, and how that ranks against all CVEs. 0.999 (99.99th pctl) FIRST EPSS
Actively exploitedWhether a source of record has confirmed attacks using it in the wild. Confirmed CISA KEV
Ransomware campaign useWhether CISA has seen ransomware operators use it. Known CISA KEV
CISA remediation deadlineThe date US federal agencies must have fixed or mitigated it. 2021-11-17 · KEV since 2021 · listed over a year CISA KEV
Public exploit moduleA module existing is not the same as active exploitation. Public module exists Metasploit
EUVD cross-referenceENISA's record: CVSS 7.5 (v3.1), assigned by apache. Listed ENISA EUVD

Description

NVD

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.

What CISA says to do

Public module

Metasploit lists the best-ranked (excellent) of 2 public modules for this CVE: Apache 2.4.49/2.4.50 Traversal RCE (multi/http/apache_normalize_path_rce). A module existing is not the same as active exploitation; see metasploit.com.