{"id":"CVE-2021-42013","kind":"vulnerability","aliases":["CVE-2021-42013"],"related":[],"title":"Apache HTTP Server: Apache HTTP Server Path Traversal Vulnerability","description":"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.","summary":"Apache HTTP Server 2.4.49 and 2.4.50 let remote attackers traverse outside Alias-mapped directories to read files and, when CGI is enabled, run commands. The flaw is actively exploited and is listed in CISA's Known Exploited Vulnerabilities catalog with ransomware use noted.","severity":"critical","cvss":9.8,"epss":0.99964,"exploited":true,"exploited_at":"2021-11-03T00:00:00+00:00","products":[{"name":"Apache HTTP Server","fixed":[],"affected":"","ecosystem":"vendor"}],"ecosystems":["vendor"],"tags":["apache-httpd","exploited","linux","ransomware","runtime","self-hosted","web-server"],"not_affected_if":["default-config","managed-hosting","version-not-2.4.49-or-2.4.50"],"how_to_check":"Run httpd -v and check whether the version is 2.4.49 or 2.4.50.\nSearch the config for ScriptAlias, mod_cgi and 'Require all granted' under Alias-mapped paths.\nCheck access logs for requests containing '/.%2e/' or '%2e%2e' paths.","fix":"Upgrade to Apache HTTP Server 2.4.51 or later, which fixes CVE-2021-41773 and CVE-2021-42013.\nIf you cannot upgrade at once, set 'Require all denied' for the root directory and disable CGI where it is not needed.","status":"open","published_at":"2021-10-07T16:15:09+00:00","first_seen_at":"2026-10-23T19:11:53+00:00","triaged_at":"2026-10-23T21:43:33+00:00","updated_at":"2026-10-23T21:57:35+00:00","category":"runtime","confidence":0.85,"triage":{"at":"2026-10-23T21:43:33Z","model":"claude-haiku-5-5","output":{"fix":"Upgrade to Apache HTTP Server 2.4.51 or later, which fixes CVE-2021-41773 and CVE-2021-42013.\nIf you cannot upgrade at once, set 'Require all denied' for the root directory and disable CGI where it is not needed.","reach":"internet","impact":"high","summary":"Apache HTTP Server 2.4.49 and 2.4.50 let remote attackers traverse outside Alias-mapped directories to read files and, when CGI is enabled, run commands. The flaw is actively exploited and is listed in CISA's Known Exploited Vulnerabilities catalog with ransomware use noted.","category":"runtime","who_cares":["apache-httpd","self-hosted","linux","web-server"],"confidence":0.85,"needs_auth":"no","worst_case":"Attacker runs arbitrary commands on the server through CGI.","analyst_note":"Confirm the affected and fixed version ranges and the vendor advisory text from httpd.apache.org/security/vulnerabilities_24.html; the sources here do not list them.","how_to_check":"Run httpd -v and check whether the version is 2.4.49 or 2.4.50.\nSearch the config for ScriptAlias, mod_cgi and 'Require all granted' under Alias-mapped paths.\nCheck access logs for requests containing '/.%2e/' or '%2e%2e' paths.","needs_analyst":true,"not_affected_if":["version-not-2.4.49-or-2.4.50","managed-hosting","default-config"],"user_interaction":"no","needs_special_setup":"yes","severity_if_unknown":"critical"},"cost_usd":0.000572,"input_tokens":2884,"output_tokens":567,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2021':11A,14A,84C '-41773':85C '-42013':12A,15A '2.4.49':35B,158C '2.4.50':37B,90C,161C 'activ':60B 'affect':156C 'alia':44B,112C 'alias':144C 'alias-lik':111C 'alias-map':43B 'allow':148C 'also':140C 'apach':1A,4A,20B,32B,87C,157C,160C 'apache':16A 'apache-httpd':19B 'attack':40B,94C,100C 'catalog':71B 'cgi':52B,137C 'cisa':66B 'code':151C 'command':56B 'configur':109C,128C 'could':95C,147C 'cve':10A,13A,83C 'default':127C 'deni':131C 'direct':114C 'directori':46B,108C,120C 'earlier':164C 'enabl':54B,141C 'execut':152C 'exploit':22B,61B,69B 'file':49B,105C,116C 'fix':81C 'flaw':58B 'found':78C 'host':28B 'http':2A,5A,17A,33B,88C 'httpd':21B 'insuffici':92C 'issu':154C 'known':68B 'let':38B 'like':113C 'linux':23B 'list':64B 'map':45B,102C 'note':75B 'outsid':42B,106C,117C 'path':7A,98C,145C 'protect':123C 'ransomwar':24B,73B 'read':48B 'remot':39B,150C 'request':133C 'requir':129C 'run':55B 'runtim':25B 'script':138C 'self':27B 'self-host':26B 'server':3A,6A,18A,31B,34B,89C 'succeed':135C 'travers':8A,41B,99C 'url':103C 'use':74B,96C 'usual':126C 'version':165C 'vulner':9A,70B 'web':30B 'web-serv':29B","nicknames":[],"mitigations":[],"who_affected":null,"tier":null,"verified":{},"analyst_revisit_at":null,"first_public_at":"2021-10-07T16:15:09+00:00","kev":{"dateAdded":"2021-11-03","dueDate":"2021-11-17","requiredAction":"Apply updates per vendor instructions.","knownRansomwareCampaignUse":"Known"},"cvss_vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","cvss_by":"nvd@nist.gov","poc_count":0,"sources":[{"source":"kev","external_id":"CVE-2021-42013","url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-42013","severity":null,"published_at":"2021-11-03T00:00:00+00:00","modified_at":null,"first_seen_at":"2026-10-23T19:11:53+00:00","fetched_at":"2026-10-25T12:39:25+00:00","note":null},{"source":"epss","external_id":"CVE-2021-42013","url":"https://api.first.org/data/v1/epss?cve=CVE-2021-42013","severity":null,"published_at":null,"modified_at":null,"first_seen_at":"2026-10-23T19:13:44+00:00","fetched_at":"2026-10-23T19:13:44+00:00","note":null},{"source":"nvd","external_id":"CVE-2021-42013","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-42013","severity":null,"published_at":"2021-10-07T16:15:09+00:00","modified_at":"2026-06-17T04:09:09+00:00","first_seen_at":"2026-10-23T21:57:35+00:00","fetched_at":"2026-10-23T21:57:35+00:00","note":null}],"documents":[],"notice":"Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}