Detects calendar (.ics) files that do not follow RFC standards by lacking required UID identifiers while containing specific calendar components (VTODO, VJOURNAL, VFREEBUSY, or VEVENT). Forged ICS calendar invites can be spoofed to seemingly originate from any sender.

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Detects inbound emails where the sender domain is less than 10 days old from untrusted senders.

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This rule identifies potential impersonation attempts involving the local part of an $org_vip email address. Specifically, it checks for cases where the local part of an $org_vip email (e.g., local_part@domain.com) appears with a different domain (e.g., local_part@foreigndomain.com). Additionally, the rule flags messages that match an $org_vip address exactly but fail authentication.

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This Attack Surface Reduction (ASR) rule matches on Dropbox notifications with recently registered reply-to domains.

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DocuSign shares which contain a reply-to address or domain that has not been previously observed by the recipient organization.

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This rule detects messages claiming to have the attendee list from a specific event, they may list various information such as the number of contacts, the demographic and sample contacts. The messages typically offer to send pricing information upon request.

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This attack surface reduction rule matches on messages from Adobe which were sent by an email address (as determined by the sender display name) which doesn't appear to have a relationship with the recipient organization.

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Attach text file is less than 1000 bytes and contains a recipients email address. Seen in the wild carrying credential phishing links.

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Detects HTML files in EML attachments from unsolicited senders.

Reduces attack surface against HTML smuggling.

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Mailer is atypical of sends from Gmail infrastructure. Observed sending callback phishing and general spam.

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Message contains use of the Dell open redirect, but the sender is not Dell.

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DocuSign shares with new reply-to addresses have been seen in recent attacks.

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Recon messages, a form of deliverability testing, are used to validate whether a recipient address is valid or not, potentially preceding an attack.

All recipients are bcc'd or undisclosed, with no links or attachments, and a short body and subject from an unknown sender.

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Recon messages, a form of deliverability testing, are used to validate whether a recipient address is valid or not, potentially preceding an attack.

There's a large number of recipients that are unknown to the organization, no links or attachments, and a short body and subject from an unknown sender.

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Recursively scans archives to detect disallowed file types. File extensions can be detected within password-protected archives.

Attackers often embed malicious files within archives to bypass email gateway controls.

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HTML attachment (or HTML attachment in attached email) is small and contains a recipients email address.

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This rule detects messages with unscannable links to cloudflare infrastructure with suspicious indicators in the subject or display name from an unsolicited sender.

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The default Microsoft Exchange Online sender domain, onmicrosoft.com, is commonly used to send unwanted and malicious email. Enable this rule in your environment if receiving email from the onmicrosoft.com domain is unexpected behaviour.

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Fake thread contains suspicious indicators, which can lead to BEC, credential phishing, and other undesirable outcomes.

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This matches on inbound Shared File notiifcation emails from Microsoft, where any link to SharePoint contains a default GoDaddy Federated Tenant Name. These have been observed being frequently abused to send credential phishing campaigns.

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This rule detects unsolicited messages containing a mix of Cyrillic and Latin characters in the subject or sender's name while excluding emails from Russian domains and specific Google Calendar notification bounce emails.

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Message contains use of the VK open redirect, but the sender is not VK. This has been exploited in the wild.

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This ASR rule detects the use of secure SharePoint links which require recipient verifcation before allowing access to the shared file. This has been observed as a method of evading automated analysis of the shared files' content.

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Detects messages with undisclosed recipients, containing links to free subdomain hosts

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Sender subject contains the display name of a user in the $org_vips list, and the sender has never been seen before.

The $org_vips list must first be manually connected to a VIP group of your upstream provider (Google Workspace and Microsoft 365 only) in order for this rule to work. Once connected, the list will be automatically synced and kept up-to-date. For more information, see the $org_vips documentation: https://docs.sublimesecurity.com/docs/configure-org_vips-list

This rule is recommended to be used on a relatively small list of VIPs, and is meant to reduce attack surface by detecting any message that matches the protected list of display names from a first-time or unsolicited sender.

Additional rule logic can be added to look for suspicious subjects, suspicious links, etc.

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Email contains Twitter shortened link (t.co) but does not originate from a Twitter domain. This is a known malicious and spam tactic.

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Sender display name matches the display name of a user in the $org_vips list, and the sender has never been seen before.

The $org_vips list must first be manually connected to a VIP group of your upstream provider (Google Workspace and Microsoft 365 only) in order for this rule to work. Once connected, the list will be automatically synced and kept up-to-date. For more information, see the $org_vips documentation: https://docs.sublimesecurity.com/docs/configure-org_vips-list

This rule is recommended to be used on a relatively small list of VIPs, and is meant to reduce attack surface by detecting any message that matches the protected list of display names from a first-time or unsolicited sender.

Additional rule logic can be added to look for suspicious subjects, suspicious links, etc.

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The sender is a known org domain and doesn't use a known org display name. SPF and DMARC verdicts are "none", which means the domain is spoofable. We then look for a combination of other suspicious signals such as a suspicious link or suspicious language.

False Positives may occur with automated sending systems that send rich text emails, in which case we can add additional signals or exclude those.

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Message contains a suspicious Recipients pattern, a link that uses a free subdomain provider, and has credential theft language on the linked page.

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Message contains a link that uses a free subdomain provider, and has a login or captcha on the page.

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A link in the body of the message downloads an archive containing a DMG file. The message is not from a common or trusted sender and is unsolicited.

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Shortened link is blocked or gated by bit.ly. Indicator of malicious email.

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Detects links in the body of an email where the linked domain is less than 10 days old from untrusted senders.

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Looks for use of the YouTube open redirect coming from someone other than YouTube.

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Potential HTML smuggling attacks in unsolicited messages. Use if passing HTML files is not normal behavior in your environment. This rule may be expanded to inspect HTML attachments for suspicious code.

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Potential HTML smuggling attacks from new senders. Use if passing HTML files is not normal behavior in your environment. This rule may be expanded to inspect HTML attachments for suspicious code.

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Message contains use of the Ticketmaster open redirect, but the sender is not Ticketmaster. This has been exploited in the wild.

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This rule identifies attachments containing file scheme links pointing to IP Addresses, a common indicator of malware distribution. It applies to various suspicious file extensions and archive formats, aiming to prevent the initiation and execution of malicious software. The rule negates firing on IP addresses governed by RFC1918 or privately allocated space.

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This rule identifies attachments containing file scheme links pointing to executable file types, a common indicator of malware distribution. It applies to various suspicious file extensions and archive formats, aiming to prevent the initiation and execution of malicious software.

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This rule is designed to detect sophisticated phishing attacks that deliver binary payloads through MS office open XML files. It identifies malicious documents containing embedded scripts or objects, either encoded in base64 or using specific JavaScript functions like createObjectURL or msSaveOrOpenBlob, which are indicative of attempts to download and execute a binary payload.

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Message contains use of the Google Web Light open redirect. Google Web Light was sunset on December 19 2022.

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RTF files can contain embedded content similar to OLE files (Microsoft Office documents.)

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The return-path header is a .ru TLD from an untrusted sender.

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Recursively scans archives and Office documents to detect remote document template injection.

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Attached Office file contains suspicious function calls or known malicious file path pattern.

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The body contains a link to a domain with Punycode characters to hide the true URL destination, or contains non-printable ASCII content.

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Detects emails containing links using Linkedin '/slink?code=xxxxx' open redirect where the email has not come from Linkedin.com

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Looks for use of the Panera Bread open redirect coming from someone other than Panera.

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Message contains use of the Samsung open redirect, but the sender is not Samsung.

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Message contains use of Slack's open redirect but the sender is not Slack.

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Message contains use of the click.snapchat.com open redirect.

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Javascript contains identifiers or strings that may attempt to execute files.

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Encrypted OLE2 (eg Microsoft Office) attachment from an unsolicited sender. Attachment encryption is a common technique used to bypass malware scanning products. Use if receiving encrypted attachments is not normal behavior in your environment.

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A file sharing link in the body sent from a suspicious sender domain.

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Message contains a notion link that contains suspicious terms. You may need to deactivate or fork this rule if your organization uses Notion.

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Sender is using a disposable email service and no one in our organization has ever sent them an email.

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Recursively scans files and archives to detect encrypted zip files.

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Recursively scans archives to detect HTML files from unsolicited senders.

HTML files can be used for HTML smuggling and embedded in archives to evade detection.

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Attackers have used the Google Translate service to deliver links to malicious sites repackaged with a translate.goog top-level domain. This rule identifies instances of Google Translate links from unsolicited senders.

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Use if passing compressed or archive files is not typical behavior in your organization. This behavior has been observed in a number of phishing campaigns.

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Recursively scans files and archives to detect RDP connection files.

Coercing a target user into connecting to an attacker-owned RDP server can expose elements of their host and potentially lead to compromise.

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