{"cveID":"CVE-2021-26855","vendorProject":"Microsoft","product":"Exchange Server","vulnerabilityName":"Microsoft Exchange Server Remote Code Execution Vulnerability","dateAdded":"2021-11-03","shortDescription":"Microsoft Exchange Server contains an unspecified vulnerability that allows for remote code execution. This vulnerability is part of the ProxyLogon exploit chain.","requiredAction":"Apply updates per vendor instructions.","dueDate":"2022-05-03","knownRansomwareCampaignUse":"Known","notes":"Reference CISA's ED 21-02 (https://www.cisa.gov/news-events/directives/ed-21-02-mitigate-microsoft-exchange-premises-product-vulnerabilities) for further guidance and requirements. Note: The due date for addressing this vulnerability aligns with the requirements outlined in ED 21-02. https://nvd.nist.gov/vuln/detail/CVE-2021-26855","cwes":["CWE-918"],"year":2021,"state":"mapped","stale_reasons":[],"mappings":[{"domain":"enterprise","cve":"CVE-2021-26855","technique":"T1133","technique_name_at_mapping":"External Remote Services","mapping_type":"exploitation_technique","capability_group":"code_execution","comments":"CVE-2021-26855 allows an unauthenticated attacker to send arbitrary HTTP requests and authenticate as the Exchange Server. The vulnerability exploits the Exchange Control Panel (ECP) via a Server-Side Request Forgery (SSRF). This would also allow the attacker to gain access to mailboxes and read sensitive information.","references":["https://www.cisa.gov/news-events/cybersecurity-advisories/aa21-062a"],"status":"complete","source_file":"kev-07.28.2025_attack-16.1-enterprise.json","attack_version":"16.1","kev_snapshot":"07/28/2025"},{"domain":"enterprise","cve":"CVE-2021-26855","technique":"T1005","technique_name_at_mapping":"Data from Local System","mapping_type":"secondary_impact","capability_group":"code_execution","comments":"CVE-2021-26855, also known as ProxyLogon, allows an unauthenticated attacker to send arbitrary HTTP requests and authenticate as the Exchange Server. The vulnerability exploits the Exchange Control Panel (ECP) via a Server-Side Request Forgery (SSRF). This would also allow the attacker to gain access to mailboxes and read sensitive information.","references":["https://www.cisa.gov/news-events/cybersecurity-advisories/aa21-062a"],"status":"complete","source_file":"kev-07.28.2025_attack-16.1-enterprise.json","attack_version":"16.1","kev_snapshot":"07/28/2025"},{"domain":"enterprise","cve":"CVE-2021-26855","technique":"T1090","technique_name_at_mapping":"Proxy","mapping_type":"primary_impact","capability_group":"code_execution","comments":"CVE-2021-26855 allows an unauthenticated attacker to send arbitrary HTTP requests and authenticate as the Exchange Server. The vulnerability exploits the Exchange Control Panel (ECP) via a Server-Side Request Forgery (SSRF). This would also allow the attacker to gain access to mailboxes and read sensitive information.","references":["https://www.cisa.gov/news-events/cybersecurity-advisories/aa21-062a"],"status":"complete","source_file":"kev-07.28.2025_attack-16.1-enterprise.json","attack_version":"16.1","kev_snapshot":"07/28/2025"},{"domain":"enterprise","cve":"CVE-2021-26855","technique":"T1505.003","technique_name_at_mapping":"Web Shell","mapping_type":"secondary_impact","capability_group":"code_execution","comments":"CVE-2021-26855, also known as ProxyLogon, allows an unauthenticated attacker to send arbitrary HTTP requests and authenticate as the Exchange Server. The vulnerability exploits the Exchange Control Panel (ECP) via a Server-Side Request Forgery (SSRF). This would also allow the attacker to gain access to mailboxes and read sensitive information.","references":["https://www.cisa.gov/news-events/cybersecurity-advisories/aa21-062a"],"status":"complete","source_file":"kev-07.28.2025_attack-16.1-enterprise.json","attack_version":"16.1","kev_snapshot":"07/28/2025"}],"techniques":[{"id":"T1005","domains":["enterprise"],"in_current_bundle":true,"live":true,"name_now":"Data from Local System","name_at_mapping":"Data from Local System","renamed":false,"revoked_by":null,"mapping_types":["secondary_impact"],"sigma_rule_count":14,"has_detection_strategy":true},{"id":"T1090","domains":["enterprise"],"in_current_bundle":true,"live":true,"name_now":"Proxy","name_at_mapping":"Proxy","renamed":false,"revoked_by":null,"mapping_types":["primary_impact"],"sigma_rule_count":22,"has_detection_strategy":true},{"id":"T1133","domains":["enterprise"],"in_current_bundle":true,"live":true,"name_now":"External Remote Services","name_at_mapping":"External Remote Services","renamed":false,"revoked_by":null,"mapping_types":["exploitation_technique"],"sigma_rule_count":20,"has_detection_strategy":true},{"id":"T1505.003","domains":["enterprise"],"in_current_bundle":true,"live":true,"name_now":"Web Shell","name_at_mapping":"Web Shell","renamed":false,"revoked_by":null,"mapping_types":["secondary_impact"],"sigma_rule_count":35,"has_detection_strategy":true}],"mapping_types":["exploitation_technique","primary_impact","secondary_impact"],"has_exploitation_technique":true,"mapping_attack_versions":["16.1"],"mapping_domains":["enterprise"],"sigma_coverage":"full","sigma_rules_tagged_cve":[],"added_after_mapping_snapshot":false,"_source":"kevmap","_built":"2026-08-23 05:47 UTC","_attack_version":"19.2"}