Attachment: PDF with EOF MD5 hash marker

calendar Sep 10, 2026  ·
Share on: linkedin copy

Detects inbound messages containing a PDF attachment whose contents match a YARA signature identifying an MD5 hash appended near the end of file. This technique is commonly used to make each generated PDF unique, helping evade hash-based detection systems.

Sublime rule (View on GitHub)

 1name: "Attachment: PDF with EOF MD5 hash marker"
 2description: "Detects inbound messages containing a PDF attachment whose contents match a YARA signature identifying an MD5 hash appended near the end of file. This technique is commonly used to make each generated PDF unique, helping evade hash-based detection systems."
 3type: "rule"
 4severity: "high"
 5source: |
 6    type.inbound
 7    and any(filter(attachments, .file_type == "pdf"),
 8            any(file.explode(.),
 9                any(.scan.yara.matches, .name in ("pdf_eof_md5_hash"))
10            )
11    )    
12attack_types:
13  - "Credential Phishing"
14  - "Malware/Ransomware"
15tactics_and_techniques:
16  - "PDF"
17  - "Evasion"
18detection_methods:
19  - "File analysis"
20  - "YARA"
21id: "b5eb01ac-b191-5536-b1b6-107e32dfd050"
to-top