{"id":"CVE-2021-41773","published":"2021-10-05T09:15:07Z","modified":"2026-06-17T04:08:53Z","title":"Apache HTTP Server Path Traversal Vulnerability","vendor":"Apache","product":"HTTP Server","tier":"core","eol":null,"description":{"text":"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.","provenance":"source","from":"NVD"},"summary":{"text":"The flaw is a path traversal weakness in the path normalization logic of Apache HTTP Server, product HTTP Server, introduced by a change in version 2.4.49. An unauthenticated remote attacker can send crafted requests over the network, with no user interaction, to map URLs to files outside the directories configured by Alias-like directives, and if those files are not protected by the default \"require all denied\" setting, the requests succeed; where CGI scripts are also enabled for the aliased paths, this can lead to remote code execution.","provenance":"ai","model":"claude-haiku-5-5","generatedAt":"2026-10-29T07:53:35Z"},"cvss":{"score":9.8,"severity":"CRITICAL","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","provenance":"source","from":"NVD"},"epss":{"score":0.99992,"percentile":0.99986,"date":"2026-10-29","provenance":"source"},"kev":{"dateAdded":"2021-11-03","dueDate":"2021-11-17","ransomware":true,"requiredAction":"Apply updates per vendor instructions.","notes":"https://nvd.nist.gov/vuln/detail/CVE-2021-41773","provenance":"source"},"vulncheckKev":{"dateAdded":"2021-09-29","exploitedFirstSeen":"2021-09-29","ransomware":true,"evidence":[{"url":"https://docs.google.com/spreadsheets/d/1lkNJ0uQwbeC1ZTRrxdtuPLCIl7mlUreoKfSIgajnSyY/edit","date":"2021-09-29"},{"url":"https://www.cve.org/CVERecord?id=CVE-2021-41773","date":"2021-10-05"},{"url":"https://www.cisa.gov/sites/default/files/feeds/known_exploited_vulnerabilities.json","date":"2021-11-03"},{"url":"https://www.countercraftsec.com/blog/post/cve-2021-41773-actively-exploited-by-h2miner/","date":"2021-11-16"},{"url":"https://unit42.paloaltonetworks.com/network-attacks-trends-august-october-2021/","date":"2021-12-21"},{"url":"https://blog.checkpoint.com/security/december-2021s-most-wanted-malware-trickbot-emotet-and-the-log4j-plague/","date":"2022-01-12"},{"url":"https://www.trendmicro.com/en_us/research/22/b/recent-cyberattacks-open-source-web-servers.html","date":"2022-02-22"},{"url":"https://www.fortinet.com/blog/threat-research/enemybot-a-look-into-keksecs-latest-ddos-botnet","date":"2022-04-12"},{"url":"https://static.tenable.com/marketing/whitepapers/Whitepaper-Ransomware_Ecosystem.pdf","date":"2022-06-22"},{"url":"https://www.cisa.gov/uscert/ncas/alerts/aa22-279a","date":"2022-10-06"}],"evidenceTotal":40,"provenance":"source"},"exploited":true,"otx":{"pulseCount":50,"pulses":[{"name":"Actively_Exploited_Kev | Oct 29, 2026","url":"https://otx.alienvault.com/pulse/6ae20c1db17e7057ae7d9ad1","created":"2026-10-28"},{"name":"Actively_Exploited_Kev | Oct 28, 2026","url":"https://otx.alienvault.com/pulse/6ae0ba7e0e2a97ff7b218819","created":"2026-10-27"},{"name":"Actively_Exploited_Kev | Oct 27, 2026","url":"https://otx.alienvault.com/pulse/6adf68b85c3e852f3c111d18","created":"2026-10-26"},{"name":"Actively_Exploited_Kev | Oct 24, 2026","url":"https://otx.alienvault.com/pulse/6adb740e397c3ad4799aa4cd","created":"2026-10-23"},{"name":"Actively_Exploited_Kev | Oct 23, 2026","url":"https://otx.alienvault.com/pulse/6ada236fcfba2dfa730ea482","created":"2026-10-22"},{"name":"Actively_Exploited_Kev | Oct 22, 2026","url":"https://otx.alienvault.com/pulse/6ad8d33a077cbb5cab524d80","created":"2026-10-21"},{"name":"Actively_Exploited_Kev | Oct 21, 2026","url":"https://otx.alienvault.com/pulse/6ad78130c4d1ac2be83a8b6d","created":"2026-10-20"},{"name":"Actively_Exploited_Kev | Oct 20, 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2 Exploit-DB entries; 138 PoC-in-GitHub repos; 2 Metasploit modules; 1 nuclei template"},{"name":"Mentioned in OTX pulses","points":3.0,"detail":"50 pulses"},{"name":"CVSS severity","points":6.86,"detail":"base score 9.8"},{"name":"End-of-life product","points":0.0,"detail":"supported or unknown"}]},"lineage":{"familyId":"fam-apache-http-server-cve-2021-41773","children":[{"from":"CVE-2021-41773","to":"CVE-2021-42013","relation":"incomplete-fix","confidence":"high","kind":"lineage","evidence":[{"kind":"text","provenance":"source","relation":"incomplete-fix","quote":"It was found that the fix for CVE-2021-41773 in Apache HTTP Server 2.4.50 was insufficient.","from":"NVD","in":"CVE-2021-42013"},{"kind":"similar","provenance":"machine","score":0.89,"basis":"same product + CWE + description similarity"}]}]}}