{"id":"CVE-2021-40438","kind":"vulnerability","aliases":["CVE-2021-40438"],"related":[],"title":"Apache Apache: Apache HTTP Server-Side Request Forgery (SSRF)","description":"A crafted request uri-path can cause mod_proxy to forward the request to an origin server choosen by the remote user. This issue affects Apache HTTP Server 2.4.48 and earlier.\n\nCISA required action: Apply updates per vendor instructions.","summary":"Apache HTTP Server's mod_proxy can be tricked by a crafted request URI into forwarding the request to a backend server the remote user picks. An attacker can use the server as a proxy to reach internal services that the server itself can access.","severity":"critical","cvss":9.0,"epss":0.99999,"exploited":true,"exploited_at":"2021-12-01T00:00:00+00:00","products":[{"name":"Apache Apache","fixed":[],"affected":"","ecosystem":"vendor"}],"ecosystems":["vendor"],"tags":["apache-httpd","exploited","ransomware","reverse-proxy","runtime","self-hosted"],"not_affected_if":["mod_proxy-not-loaded","version-above-2.4.48"],"how_to_check":"Run httpd -v and check whether the version is 2.4.48 or earlier.\nCheck whether mod_proxy is loaded (httpd -M | grep proxy) and whether ProxyPass or ProxyPassMatch directives are present in the config.","fix":"Upgrade Apache HTTP Server to a release later than 2.4.48 per the vendor instructions.","status":"open","published_at":"2021-09-16T15:15:07+00:00","first_seen_at":"2026-10-23T19:11:53+00:00","triaged_at":"2026-10-23T21:31:57+00:00","updated_at":"2026-10-23T21:57:35+00:00","category":"runtime","confidence":0.8,"triage":{"at":"2026-10-23T21:31:57Z","model":"claude-haiku-5-5","output":{"fix":"Upgrade Apache HTTP Server to a release later than 2.4.48 per the vendor instructions.\nunknown","reach":"internet","impact":"medium","summary":"Apache HTTP Server's mod_proxy can be tricked by a crafted request URI into forwarding the request to a backend server the remote user picks. An attacker can use the server as a proxy to reach internal services that the server itself can access.","category":"runtime","who_cares":["apache-httpd","self-hosted","reverse-proxy"],"confidence":0.8,"needs_auth":"no","worst_case":"Attacker reaches internal services through the server, enabling SSRF into private networks","analyst_note":"Confirm the exact fixed version from the Apache security advisory for CVE-2021-40438 and whether ProxyPass-based configs are the only exposure.","how_to_check":"Run httpd -v and check whether the version is 2.4.48 or earlier.\nCheck whether mod_proxy is loaded (httpd -M | grep proxy) and whether ProxyPass or ProxyPassMatch directives are present in the config.\nunknown","needs_analyst":true,"not_affected_if":["mod_proxy-not-loaded","version-above-2.4.48"],"user_interaction":"no","needs_special_setup":"yes","severity_if_unknown":"high"},"cost_usd":0.000514,"input_tokens":2844,"output_tokens":460,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2021':12A,15A '-40438':13A,16A '2.4.48':105C 'access':75B 'action':110C 'affect':101C 'apach':1A,2A,3A,20B,31B,102C 'apache':17A,18A 'apache-httpd':19B 'appli':111C 'attack':58B 'backend':51B 'caus':83C 'choosen':94C 'cisa':108C 'craft':42B,77C 'cve':11A,14A 'earlier':107C 'exploit':22B 'forgeri':9A 'forward':46B,87C 'host':30B 'http':4A,32B,103C 'httpd':21B 'instruct':115C 'intern':68B 'issu':100C 'mod':35B,84C 'origin':92C 'path':81C 'per':113C 'pick':56B 'proxi':26B,36B,65B,85C 'ransomwar':23B 'reach':67B 'remot':54B,97C 'request':8A,43B,48B,78C,89C 'requir':109C 'revers':25B 'reverse-proxi':24B 'runtim':27B 'self':29B 'self-host':28B 'server':6A,33B,52B,62B,72B,93C,104C 'server-sid':5A 'servic':69B 'side':7A 'ssrf':10A 'trick':39B 'updat':112C 'uri':44B,80C 'uri-path':79C 'use':60B 'user':55B,98C 'vendor':114C","nicknames":[],"mitigations":[],"who_affected":null,"tier":null,"verified":{},"analyst_revisit_at":null,"first_public_at":"2021-09-16T15:15:07+00:00","kev":{"dateAdded":"2021-12-01","dueDate":"2021-12-15","requiredAction":"Apply updates per vendor instructions.","knownRansomwareCampaignUse":"Known"},"cvss_vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H","cvss_by":"nvd@nist.gov","poc_count":0,"sources":[{"source":"kev","external_id":"CVE-2021-40438","url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-40438","severity":null,"published_at":"2021-12-01T00:00:00+00:00","modified_at":null,"first_seen_at":"2026-10-23T19:11:53+00:00","fetched_at":"2026-10-25T16:39:49+00:00","note":null},{"source":"epss","external_id":"CVE-2021-40438","url":"https://api.first.org/data/v1/epss?cve=CVE-2021-40438","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-2021-40438","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-40438","severity":null,"published_at":"2021-09-16T15:15:07+00:00","modified_at":"2026-08-06T05:16:35+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"}