{"id":"CVE-2021-41773","kind":"vulnerability","aliases":["CVE-2021-41773"],"related":[],"title":"Apache HTTP Server: Apache HTTP Server Path Traversal Vulnerability","description":"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.","summary":"Apache HTTP Server 2.4.49 allows path traversal through crafted URLs, letting remote attackers read files outside the web root. If CGI scripts are enabled, the flaw can lead to remote code execution on the server.","severity":"critical","cvss":9.8,"epss":0.99992,"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"],"not_affected_if":["default-config","managed-hosting"],"how_to_check":"Run httpd -v and check whether the version is 2.4.49.\nCheck whether CGI is enabled, for example with grep -rn 'ScriptAlias\\|mod_cgi' on the Apache config directory.","fix":"Upgrade Apache HTTP Server to a fixed release; this CVE's original patch was insufficient, so follow CVE-2021-42013 for the complete fix.","status":"open","published_at":"2021-10-05T09:15:07+00:00","first_seen_at":"2026-10-23T19:11:53+00:00","triaged_at":"2026-10-23T21:43:29+00:00","updated_at":"2026-10-23T21:57:35+00:00","category":"runtime","confidence":0.8,"triage":{"at":"2026-10-23T21:43:29Z","model":"claude-haiku-5-5","output":{"fix":"Upgrade Apache HTTP Server to a fixed release; this CVE's original patch was insufficient, so follow CVE-2021-42013 for the complete fix.\nunknown","reach":"internet","impact":"high","summary":"Apache HTTP Server 2.4.49 allows path traversal through crafted URLs, letting remote attackers read files outside the web root. If CGI scripts are enabled, the flaw can lead to remote code execution on the server.","category":"runtime","who_cares":["apache-httpd","self-hosted","linux"],"confidence":0.8,"needs_auth":"no","worst_case":"Attacker reads server files and runs commands via CGI scripts","analyst_note":"Confirm the affected and fixed version ranges from the Apache security advisory and point the team to CVE-2021-42013 for the complete fix.","how_to_check":"Run httpd -v and check whether the version is 2.4.49.\nCheck whether CGI is enabled, for example with grep -rn 'ScriptAlias\\|mod_cgi' on the Apache config directory.\nunknown","needs_analyst":true,"not_affected_if":["managed-hosting","default-config"],"user_interaction":"no","needs_special_setup":"yes","severity_if_unknown":"critical"},"cost_usd":0.00051,"input_tokens":2895,"output_tokens":441,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2021':11A,14A,174C '-41773':12A,15A '-42013':175C '2.4.49':32B,79C,155C '2.4.50':166C 'affect':153C 'alia':99C 'alias':131C 'alias-lik':98C 'allow':33B,135C 'also':127C 'apach':1A,4A,20B,29B,76C,154C,163C 'apache':16A 'apache-httpd':19B 'attack':41B,81C,87C 'cgi':49B,124C 'chang':70C 'code':59B,138C 'configur':96C,115C 'could':82C,134C 'craft':37B 'cve':10A,13A,173C 'default':114C 'deni':118C 'direct':101C 'directori':95C,107C 'earlier':158C 'enabl':52B,128C 'execut':60B,139C 'exploit':22B,146C 'file':43B,92C,103C 'fix':161C 'flaw':54B,65C 'found':67C,168C 'host':28B 'http':2A,5A,17A,30B,77C,164C 'httpd':21B 'incomplet':171C 'issu':141C,151C 'known':143C 'lead':56B 'let':39B 'like':100C 'linux':23B 'made':71C 'map':89C 'normal':74C 'outsid':44B,93C,104C 'path':7A,34B,73C,85C,132C 'protect':110C 'ransomwar':24B 'read':42B 'remot':40B,58B,137C 'request':120C 'requir':116C 'root':47B 'runtim':25B 'script':50B,125C 'see':172C 'self':27B 'self-host':26B 'server':3A,6A,18A,31B,63B,78C,165C 'succeed':122C 'travers':8A,35B,86C 'url':38B,90C 'use':83C 'usual':113C 'version':159C 'vulner':9A 'web':46B 'wild':149C","nicknames":[],"mitigations":[],"who_affected":null,"tier":null,"verified":{},"analyst_revisit_at":null,"first_public_at":"2021-10-05T09:15:07+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-2021-41773","url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-41773","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":"2026-10-25T17:39:58+00:00","note":null},{"source":"epss","external_id":"CVE-2021-41773","url":"https://api.first.org/data/v1/epss?cve=CVE-2021-41773","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-2021-41773","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-41773","severity":null,"published_at":"2021-10-05T09:15:07+00:00","modified_at":"2026-06-17T04:08:53+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"}