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High Severity

Attachment: HTML with obfuscation and recipient's email in JavaScript strings

Labels

Credential Phishing
HTML smuggling
Scripting
Archive analysis
File analysis
HTML analysis
Javascript analysis

Description

Attached HTML file contains JavaScript code with suspicious identifiers like 'atob' or 'decrypt', as well as the recipient's email address embedded within the JavaScript

References

No references.

Sublime Security
Created Aug 29th, 2023 • Last updated Apr 10th, 2025
Feed Source
Sublime Core Feed
Source
GitHub
type.inbound
and any(attachments,
        (
          .file_extension in~ ("html", "htm", "shtml", "dhtml", "xhtml")
          or (
            .file_extension is null
            and .file_type == "unknown"
            and .content_type == "application/octet-stream"
          )
          or .file_extension in~ $file_extensions_common_archives
          or .file_type == "html"
          or .content_type == "text/html"
        )
        and .size < 1000000
        and any(file.explode(.),
                // suspicious identifiers
                any([.scan.strings.strings, .scan.javascript.identifiers],
                    any(., strings.like(., "*atob*", "*decrypt*"))
                )
        )
        // Recipients address found in javascript
        and any(file.explode(.),
                (
                  any(recipients.to,
                      (
                        any(..scan.javascript.strings,
                            strings.icontains(., ..email.email)
                        )
                        or any(..scan.strings.strings,
                               strings.icontains(., ..email.email)
                        )
                      )
                      and (
                        .email.domain.valid
                        or strings.icontains(.display_name, "undisclosed")
                      )
                  )
                )
        )
        // Negating Cisco Secure Email Encryption
        and not any(file.explode(.),
                    any(.scan.javascript.strings,
                        strings.contains(., "Cisco Registered Envelope Service")
                        or strings.contains(., "https://res.cisco.com:443")
                    )
        )
)
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