Link: PDF file disguised as HTML page

calendar Jun 5, 2026  ·
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Detects inbound messages containing links that appear to reference PDF files but are actually HTML pages, indicated by URLs ending with '.pdf' followed by additional characters and '.html'. This technique is commonly used to bypass security filters and deceive recipients into believing they are accessing a legitimate PDF document.

Sublime rule (View on GitHub)

 1name: "Link: PDF file disguised as HTML page"
 2description: "Detects inbound messages containing links that appear to reference PDF files but are actually HTML pages, indicated by URLs ending with '.pdf' followed by additional characters and '.html'. This technique is commonly used to bypass security filters and deceive recipients into believing they are accessing a legitimate PDF document."
 3type: "rule"
 4severity: "medium"
 5source: |
 6  type.inbound
 7  and any(body.current_thread.links,
 8          regex.icontains(.href_url.path, '\.pdf[^/]*\.html$')
 9  )   
10attack_types:
11  - "Credential Phishing"
12  - "Malware/Ransomware"
13tactics_and_techniques:
14  - "Evasion"
15  - "PDF"
16detection_methods:
17  - "URL analysis"
18  - "Content analysis"
19id: "aa1a842d-ddd9-5e0e-8f17-bbcab4818195"
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