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Description

Qakbot double Base64 encodes zip files within their HTML smuggling email attachments. This leads to predictable file header strings appearing in the HTML string content.

@ajpc500
Created Aug 17th, 2023 • Last updated Aug 5th, 2025
Source
type.inbound
and (
  profile.by_sender().prevalence in ("new", "outlier")
  or (
    profile.by_sender().any_messages_malicious_or_spam
    and not profile.by_sender().any_messages_benign
  )
)
and any(attachments,
        .file_extension in ("html", "htm")
        and any(file.explode(.),
                any(.scan.strings.strings,
                    strings.ilike(.,
                                  // Double Base64 encoded zips
                                  "*VUVzREJCUUFBUUFJQ*",
                                  "*VFc0RCQlFBQVFBSU*",
                                  "*VRXNEQkJRQUFRQUlB*",
                                  // Reversed base64 strings double encoded zips
                                  "*QJFUUBFUUCJERzVUV*",
                                  "*USBFVQBFlQCR0cFV*",
                                  "*BlUQRFUQRJkQENXRV*"
                    )
                )
        )
)
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