{"id":"d443095b-a221-4957-a2c4-cd1756c9b747","title":"Suspicious Base64 Encoded User-Agent","description":"Detects suspicious encoded User-Agent strings, as seen used by some malware.","author":"Nasreddine Bencherchali (Nextron Systems)","status":"test","level":"medium","date":"2023-05-04","modified":"","tags":["attack.command-and-control","attack.t1071.001"],"technique_ids":["T1071.001"],"logsource":{"category":"proxy"},"falsepositives":["Unknown"],"references":["https://deviceatlas.com/blog/list-of-user-agent-strings#desktop"],"source_path":"rules/web/proxy_generic/proxy_ua_base64_encoded.yml","source_sha256":"ced7c6147ac7f7553148d3d6e33d5e276462cb30cc0c479aeb48df41f138de74","source_url":"https://github.com/anpa1200/sigma/blob/b249e9683190cffdcaf188ccbfb90bf4759844e1/rules/web/proxy_generic/proxy_ua_base64_encoded.yml","license":"Detection Rule License 1.1","license_url":"https://github.com/SigmaHQ/Detection-Rule-License/blob/main/LICENSE.Detection.Rules.md","yaml":"title: Suspicious Base64 Encoded User-Agent\nid: d443095b-a221-4957-a2c4-cd1756c9b747\nrelated:\n    - id: 894a8613-cf12-48b3-8e57-9085f54aa0c3\n      type: derived\nstatus: test\ndescription: Detects suspicious encoded User-Agent strings, as seen used by some malware.\nreferences:\n    - https://deviceatlas.com/blog/list-of-user-agent-strings#desktop\nauthor: Nasreddine Bencherchali (Nextron Systems)\ndate: 2023-05-04\ntags:\n    - attack.command-and-control\n    - attack.t1071.001\nlogsource:\n    category: proxy\ndetection:\n    selection:\n        c-useragent|startswith:\n            - 'Q2hyb21l' # Chrome Encoded with offset to not include padding\n            - 'QXBwbGVXZWJLaX' # AppleWebKit Encoded with offset to not include padding\n            - 'RGFsdmlr' # Dalvik Encoded with offset to not include padding\n            - 'TW96aWxsY'  # Mozilla Encoded with offset to not include padding (as used by YamaBot)\n    condition: selection\nfalsepositives:\n    - Unknown\nlevel: medium\n","validation":"yaml_parsed_not_backend_compiled_or_live_validated","techniques":[{"key":"enterprise/T1071.001","id":"T1071.001","name":"Web Protocols","page":"techniques/enterprise/T1071.001/"}],"data_path":"data/detection-rules/d443095b-a221-4957-a2c4-cd1756c9b747.json","kind":"sigma"}