sublimemediumRule

Attachment: Link file with UNC path

Attached link file contains a UNC path. This can be used to relay NTLM password hashes; Windows will attempt to authenticate against the path even without the file being opened.

MITRE ATT&CK

T1566 T1566.001 T1566.002 T1598 T1036 T1027

defense-evasion

Detection Query

type.inbound
and any(attachments,
        .file_extension in ("lnk", "url")
        and any(file.explode(.),
                any(.scan.strings.strings,
                    regex.icontains(.,
                                    '\\\\([a-zA-Z0-9_:%.$-]+)\\([a-zA-Z0-9_:%.$-]+)'
                    )
                ) // normal UNC paths
                or any(.scan.strings.strings,
                       regex.icontains(.,
                                       '%5C%5C([a-zA-Z0-9_:%.$-]+)%5C([a-zA-Z0-9_:%.$-]+)'
                       )
                ) // percent-encoded UNC paths
        )
)

Data Sources

Email MessagesEmail HeadersEmail Attachments

Platforms

References

https://twitter.com/fuzz_sh/status/1640041674058416129

Raw Content

name: "Attachment: Link file with UNC path"
description: |
  Attached link file contains a UNC path. This can be used to relay NTLM password hashes; Windows will attempt to authenticate against the path even without the file being opened.
references:
  - "https://twitter.com/fuzz_sh/status/1640041674058416129"
type: "rule"
severity: "medium"
source: |
  type.inbound
  and any(attachments,
          .file_extension in ("lnk", "url")
          and any(file.explode(.),
                  any(.scan.strings.strings,
                      regex.icontains(.,
                                      '\\\\([a-zA-Z0-9_:%.$-]+)\\([a-zA-Z0-9_:%.$-]+)'
                      )
                  ) // normal UNC paths
                  or any(.scan.strings.strings,
                         regex.icontains(.,
                                         '%5C%5C([a-zA-Z0-9_:%.$-]+)%5C([a-zA-Z0-9_:%.$-]+)'
                         )
                  ) // percent-encoded UNC paths
          )
  )
attack_types:
  - "Credential Phishing"
tactics_and_techniques:
  - "Evasion"
  - "LNK"
detection_methods:
  - "File analysis"
id: "3b7ee0fb-3540-51b6-a5db-9b21fdd3c9af"