cbcvebase.
CVE-2021-42013
published 2021-10-07

CVE-2021-42013: It was found that the fix for CVE-2021-41773 in Apache HTTP Server 2.4.50 was insufficient. An attacker could use a path traversal attack to map URLs to files…

PriorityP199critical9.8CVSS 3.1
AVNACLPRNUINSUCHIHAH
KEVITWEXPLOITRansomwareInitial access
CISA Known Exploited Vulnerabilitydue 2021-11-17
Exploited in the wild
EPSS
99.96%
100.0th percentile
It was found that the fix for CVE-2021-41773 in Apache HTTP Server 2.4.50 was insufficient. 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 only affects Apache 2.4.49 and Apache 2.4.50 and not earlier versions.

Affected

13 ranges
VendorProductVersion rangeFixed in
apachehttp_server
apachehttp_server
apache_software_foundationapache_http_server
apache_software_foundationapache_http_server
debianapache2< apache2 2.4.51-1 (bookworm)apache2 2.4.51-1 (bookworm)
debianapache2< apache2 2.4.50-1 (bookworm)apache2 2.4.50-1 (bookworm)
fedoraprojectfedora
fedoraprojectfedora
oracleinstantis_enterprisetrack
oracleinstantis_enterprisetrack
oracleinstantis_enterprisetrack
oraclejd_edwards_enterpriseone_tools< 9.2.6.09.2.6.0
oraclesecure_backup< 18.1.0.1.018.1.0.1.0

Detection & IOCsextracted from sources · hover to see the quote

path/etc/passwd
path/bin/sh
path/etc/services
path/etc/hosts
snort
SID 58276
snort
Snort 3 SID 300053
snort
SID 58356 - 58361
  • Monitor HTTP requests for path traversal patterns targeting /etc/passwd and /bin/sh, which are the most commonly observed exploitation targets for CVE-2021-42013.
  • Alert on HTTP requests using cURL as the user agent combined with path traversal sequences against Apache 2.4.49/2.4.50 servers.
  • Also monitor for path traversal probes targeting /etc/services and /etc/hosts in addition to /etc/passwd and /bin/sh.
  • Identify Apache HTTP Server installations running versions 2.4.49 or 2.4.50 as exclusively vulnerable; earlier versions are not affected.
  • Scanning activity for CVE-2021-42013 has been attributed to Alibaba Cloud ISPs; monitor for inbound scanning from those netblocks.
  • ·CVE-2021-42013 is only exploitable if files outside the document root are not protected by 'require all denied'; servers with this default protection in place are not vulnerable to file disclosure.
  • ·Remote code execution via CVE-2021-42013 additionally requires CGI scripts to be enabled on the aliased paths.
  • ·Only a small fraction of Apache installations are actually running the vulnerable versions (2.4.49 or 2.4.50), estimated at less than 1% of the overall Apache install base.

CVSS provenance

nvdv3.19.8CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
nvdv2.07.5HIGHAV:N/AC:L/Au:N/C:P/I:P/A:P
osv9.8CRITICAL
vulncheck9.8CRITICAL
cisa9.8CRITICAL
vendor_debian9.8CRITICAL
vendor_oracle9.8CRITICAL
vendor_redhat9.8CRITICAL
vendor_cisco7.5HIGH
CVEs like this are exactly what “Exploited This Week” covers.

Every Monday: what got weaponized or added to CISA KEV in the last seven days — each CVE cross-linked to its PoC, Nuclei template, and detection rule. Free, one email a week, unsubscribe in one click.