{"id":"CVE-2021-22991","published":"2021-03-31T18:15:14Z","modified":"2026-06-17T03:38:10Z","title":"F5 BIG-IP Traffic Management Microkernel Buffer Overflow","vendor":"F5","product":"BIG-IP Traffic Management Microkernel","tier":"core","eol":null,"description":{"text":"On BIG-IP versions 16.0.x before 16.0.1.1, 15.1.x before 15.1.2.1, 14.1.x before 14.1.4, 13.1.x before 13.1.3.6, and 12.1.x before 12.1.5.3, undisclosed requests to a virtual server may be incorrectly handled by the Traffic Management Microkernel (TMM) URI normalization, which may trigger a buffer overflow, resulting in a DoS attack. In certain situations, it may theoretically allow bypass of URL based access control or remote code execution (RCE). Note: Software versions which have reached End of Software Development (EoSD) are not evaluated.","provenance":"source","from":"NVD"},"summary":{"text":"The F5 BIG-IP Traffic Management Microkernel (TMM) contains a buffer overflow flaw in its URI normalization handling of requests sent to virtual servers. An attacker who can send undisclosed requests to a virtual server over the network can trigger the overflow with no authentication or user interaction, which may cause a denial of service and, in certain situations, theoretically allow bypass of URL-based access control or remote code execution.","provenance":"ai","model":"claude-haiku-5-5","generatedAt":"2026-10-23T07:12:02Z"},"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":0.62421,"percentile":0.99183,"date":"2026-10-29","provenance":"source"},"kev":{"dateAdded":"2022-01-18","dueDate":"2022-02-01","ransomware":false,"requiredAction":"Apply updates per vendor instructions.","notes":"https://nvd.nist.gov/vuln/detail/CVE-2021-22991","provenance":"source"},"vulncheckKev":{"dateAdded":"2021-06-01","exploitedFirstSeen":"2021-06-01","ransomware":false,"evidence":[{"url":"https://unit42.paloaltonetworks.com/network-attack-trends-february-april-2021/","date":"2021-06-01"},{"url":"https://www.fortinet.com/blog/threat-research/the-ghosts-of-mirai","date":"2021-06-24"},{"url":"https://www.cisa.gov/sites/default/files/feeds/known_exploited_vulnerabilities.json","date":"2022-01-18"}],"evidenceTotal":3,"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, 2026","url":"https://otx.alienvault.com/pulse/6ad62f63c24a405a3423cc13","created":"2026-10-19"},{"name":"Actively_Exploited_Kev | Oct 19, 2026","url":"https://otx.alienvault.com/pulse/6ad4dda174e5797d0bd238b7","created":"2026-10-18"},{"name":"Actively_Exploited_Kev | Oct 18, 2026","url":"https://otx.alienvault.com/pulse/6ad38c22e1848f8189d1c121","created":"2026-10-17"}],"provenance":"machine"},"cwes":[{"id":"CWE-119","name":"Improper Restriction of Operations within the Bounds of a Memory Buffer"}],"references":[{"url":"https://support.f5.com/csp/article/K56715231","tags":["Vendor Advisory"]},{"url":"https://support.f5.com/csp/article/K56715231","tags":["Vendor Advisory"]},{"url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-22991","tags":["US Government Resource"]}],"techniques":[{"id":"T1190","name":"Exploit Public-Facing Application","tactics":["initial-access"],"provenance":"ai","basis":"ai-mapping","bases":["ai-mapping"],"basisDetail":"claude-haiku-5-5: Exploited via crafted requests to public virtual server","mappingType":"exploitation_technique","evidence":[{"from":"description","quote":"undisclosed requests to a virtual server may be incorrectly handled","start":141,"end":208}],"model":"claude-haiku-5-5","confidence":"medium","confidenceNote":"AI-mapped from the description (quote-validated, not expert-reviewed)"},{"id":"T1059","name":"Command and Scripting Interpreter","tactics":["execution"],"provenance":"ai","basis":"ai-mapping","bases":["ai-mapping"],"basisDetail":"claude-haiku-5-5: Remote code execution explicitly stated","mappingType":"primary_impact","evidence":[{"from":"description","quote":"allow bypass of URL based access control or remote code execution (RCE)","start":380,"end":451}],"model":"claude-haiku-5-5","confidence":"medium","confidenceNote":"AI-mapped from the description (quote-validated, not expert-reviewed)"},{"id":"T1499.004","name":"Application or System Exploitation","tactics":["impact"],"provenance":"ai","basis":"ai-mapping","bases":["ai-mapping"],"basisDetail":"claude-haiku-5-5: Buffer overflow causes denial of service","mappingType":"primary_impact","evidence":[{"from":"description","quote":"may trigger a buffer overflow, resulting in a DoS attack","start":278,"end":334}],"model":"claude-haiku-5-5","confidence":"medium","confidenceNote":"AI-mapped from the description (quote-validated, not expert-reviewed)"}],"reports":[],"affected":[],"advisories":[],"euvd":{"id":"EUVD-2021-10109","url":"https://euvd.enisa.europa.eu/vulnerability/EUVD-2021-10109","exploited":true,"exploitedSince":"2022-01-18","provenance":"source"},"exploits":[],"exploitSources":null,"exploitRefs":[],"flow":[{"stage":"exploitation","techniques":["T1190"],"provenance":"ai"},{"stage":"primary","techniques":["T1059","T1499.004"],"provenance":"ai"}],"timeline":[{"date":"2021-03-31","kind":"published","label":"Published (NVD)","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-22991","provenance":"source"},{"date":"2021-06-01","kind":"exploited-reported","label":"Exploitation first reported (VulnCheck KEV evidence)","url":"https://unit42.paloaltonetworks.com/network-attack-trends-february-april-2021/","provenance":"source"},{"date":"2022-01-18","kind":"kev","label":"Added to CISA KEV","url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","provenance":"source"},{"date":"2022-01-18","kind":"euvd-exploited","label":"ENISA EUVD: exploited","url":"https://euvd.enisa.europa.eu/vulnerability/EUVD-2021-10109","provenance":"source"}],"speed":{"daysToPublicExploit":null,"firstExploitFrom":null,"daysToKev":293},"priority":{"score":64.7,"factors":[{"name":"In a KEV catalog","points":35.0,"detail":"listed in CISA KEV and VulnCheck KEV"},{"name":"Recent KEV listing","points":0.0,"detail":"added 1976 days ago"},{"name":"Known ransomware use","points":0.0,"detail":"not known"},{"name":"EPSS percentile","points":19.84,"detail":"percentile 0.9918"},{"name":"Named in threat reports","points":0.0,"detail":"0 reports"},{"name":"Public exploit code","points":0.0,"detail":"none 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