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Detectionmediumtest

Suspicious Base64 Encoded User-Agent

Detects suspicious encoded User-Agent strings, as seen used by some malware.

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Nasreddine Bencherchali (Nextron Systems)Created Thu May 04d443095b-a221-4957-a2c4-cd1756c9b747web
Log Source
Proxy Log
CategoryProxy Log← raw: proxy
Detection Logic
Detection Logic1 selector
detection:
    selection:
        c-useragent|startswith:
            - 'Q2hyb21l' # Chrome Encoded with offset to not include padding
            - 'QXBwbGVXZWJLaX' # AppleWebKit Encoded with offset to not include padding
            - 'RGFsdmlr' # Dalvik Encoded with offset to not include padding
            - 'TW96aWxsY'  # Mozilla Encoded with offset to not include padding (as used by YamaBot)
    condition: selection
False Positives
Unknown

False positive likelihood has not been assessed. Additional context may be needed during triage.

References
1
Resolving title…
deviceatlas.com
MITRE ATT&CK
Related Rules
DerivedDetectionmedium

Potential Base64 Encoded User-Agent

Detects User Agent strings that end with an equal sign, which can be a sign of base64 encoding.

This rule was derived from the related rule - both detect similar activity with different scope.

Rule Metadata
Rule ID
d443095b-a221-4957-a2c4-cd1756c9b747
Status
test
Level
medium
Type
Detection
Created
Thu May 04
Author
Nasreddine Bencherchali (Nextron Systems)
Path
rules/web/proxy_generic/proxy_ua_base64_encoded.yml
Raw Tags
attack.command-and-controlattack.t1071.001
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