Known exploited vulnerability
CVE-2021-41773
The short answer
CVE-2021-41773 affects Apache Software Foundation Apache HTTP Server and is rated critical (CVSS 9.8). CISA added it to the Known Exploited Vulnerabilities catalog on 2021-11-03: attackers are using it, so patch it first. The vendor has linked a patch.
What it is
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.
Weakness: CWE-22.
Severity
9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Exploited (CISA KEV)
Yes, since Nov 3, 2021
Federal due date Nov 17, 2021
EPSS, next 30 days
100%
Higher than 100% of scored CVEs
How it can be exploited
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- High
- Integrity impact
- High
- Availability impact
- High
What CISA says to do
Apply updates per vendor instructions.
Affected products
Apache HTTP Server. NVD's record lists the exact affected versions.
References
- httpd.apache.org/security/vulnerabilities_24.html Release NotesVendor Advisory
- lists.apache.org/thread.html/r17a4c6ce9aff662efd9459e9d1850ab4a611cb23392fc68264c72cb3%40%3Ccvs.httpd.apache.org%3E Mailing ListPatch
- lists.apache.org/thread.html/r6abf5f2ba6f1aa8b1030f95367aaf17660c4e4c78cb2338aee18982f%40%3Cusers.httpd.apache.org%3E Mailing List
- lists.apache.org/thread.html/r7c795cd45a3384d4d27e57618a215b0ed19cb6ca8eb070061ad5d837%40%3Cannounce.apache.org%3E Mailing List
- lists.apache.org/thread.html/r98d704ed4377ed889d40479db79ed1ee2f43b2ebdd79ce84b042df45%40%3Cannounce.apache.org%3E Mailing List
- lists.apache.org/thread.html/rb5b0e46f179f60b0c70204656bc52fcb558e961cb4d06a971e9e3efb%40%3Cusers.httpd.apache.org%3E Mailing List
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RMIIEFINL6FUIOPD2A3M5XC6DH45Y3CC/ Release Notes
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/WS5RVHOIIRECG65ZBTZY7IEJVWQSQPG3/ Release Notes
- security.gentoo.org/glsa/202208-20 Third Party Advisory
- security.netapp.com/advisory/ntap-20211029-0009/ Third Party Advisory
- tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-apache-httpd-pathtrv-LAzg68cZ Third Party Advisory
- www.oracle.com/security-alerts/cpujan2022.html PatchThird Party Advisory
Questions
Is CVE-2021-41773 being exploited?
Yes. CISA added CVE-2021-41773 to its Known Exploited Vulnerabilities catalog on 2021-11-03, with a federal remediation due date of 2021-11-17. CISA lists it as used in ransomware campaigns.
How do I fix CVE-2021-41773?
CISA's required action: Apply updates per vendor instructions.
From NVD, CISA KEV, FIRST EPSS and OSV.dev, checked . Status on NVD: Analyzed. The description is NVD's text, quoted as published.
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