HTTP Request to Low Reputation TLD or Suspicious File Extension

Status: experimental
Severity: medium
Log source: product zeek, service http
Author: @signalblur, Corelight
Source: github.com/SigmaHQ/sigma

Detects HTTP requests to low reputation TLDs (e.g. .xyz, .top, .ru) or ending in suspicious file extensions (.exe, .dll, .hta), which may indicate malicious activity.

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	No specific technique
Command & Control	No specific technique

Rule body yaml

title: HTTP Request to Low Reputation TLD or Suspicious File Extension
id: 68c2c604-92ad-468b-bf4a-aac49adad08c
status: experimental
description: |
    Detects HTTP requests to low reputation TLDs (e.g. .xyz, .top, .ru) or ending in suspicious file extensions (.exe, .dll, .hta), which may indicate malicious activity.
references:
    - https://www.howtogeek.com/137270/50-file-extensions-that-are-potentially-dangerous-on-windows
    - https://www.spamhaus.org/reputation-statistics/cctlds/domains/
author: '@signalblur, Corelight'
date: 2025-02-26
tags:
    - attack.initial-access
    - attack.command-and-control
logsource:
    product: zeek
    service: http
detection:
    # Suspicious TLD in the 'host' field OR malicious file extension in the 'uri' field.
    selection_suspicious_tld:
        host|endswith:
            - '.bid'
            - '.by'
            - '.cf'
            - '.click'
            - '.cm'
            - '.ga'
            - '.gq'
            - '.ir'
            - '.kp'
            - '.loan'
            - '.ml'
            - '.mm'
            - '.party'
            - '.pw'
            - '.ru'
            - '.su'
            - '.sy'
            - '.tk'
            - '.top'
            - '.tv'
            - '.ve'
            - '.work'
            - '.xyz'
    selection_malicious_ext:
        uri|endswith:
            - '.bat'
            - '.bin'
            - '.cmd'
            - '.cpl'
            - '.dll'
            - '.dylib'
            - '.elf'
            - '.exe'
            - '.hta'
            - '.iso'
            - '.jar'
            - '.js'
            - '.lnk'
            - '.msi'
            - '.pif'
            - '.ps1'
            - '.py'
            - '.reg'
            - '.scr'
            - '.sh'
            - '.so'
            - '.vbs'
            - '.wsf'
    selection_malicious_mime:
        resp_mime_types:
            - 'application/vnd.microsoft.portable-executable'
            - 'application/x-bat'
            - 'application/x-dosexec'
            - 'application/x-elf'
            - 'application/x-iso9660-image'
            - 'application/x-java-archive'
            - 'application/x-ms-shortcut'
            - 'application/x-msdos-program'
            - 'application/x-msdownload'
            - 'application/x-python-code'
            - 'application/x-sh'
    condition: selection_suspicious_tld and 1 of selection_malicious_*
falsepositives:
    - Rare legitimate software downloads from low quality TLDs
level: medium

Stages and Predicates

Stage 0: `condition`

selection_suspicious_tld and 1 of selection_malicious_*

Stage 1: `selection_suspicious_tld`

selection_suspicious_tld:
    host|endswith:
        - '.bid'
        - '.by'
        - '.cf'
        - '.click'
        - '.cm'
        - '.ga'
        - '.gq'
        - '.ir'
        - '.kp'
        - '.loan'
        - '.ml'
        - '.mm'
        - '.party'
        - '.pw'
        - '.ru'
        - '.su'
        - '.sy'
        - '.tk'
        - '.top'
        - '.tv'
        - '.ve'
        - '.work'
        - '.xyz'

Stage 2: `selection_malicious_ext`

selection_malicious_ext:
    uri|endswith:
        - '.bat'
        - '.bin'
        - '.cmd'
        - '.cpl'
        - '.dll'
        - '.dylib'
        - '.elf'
        - '.exe'
        - '.hta'
        - '.iso'
        - '.jar'
        - '.js'
        - '.lnk'
        - '.msi'
        - '.pif'
        - '.ps1'
        - '.py'
        - '.reg'
        - '.scr'
        - '.sh'
        - '.so'
        - '.vbs'
        - '.wsf'

Stage 3: `selection_malicious_mime`

selection_malicious_mime:
    resp_mime_types:
        - 'application/vnd.microsoft.portable-executable'
        - 'application/x-bat'
        - 'application/x-dosexec'
        - 'application/x-elf'
        - 'application/x-iso9660-image'
        - 'application/x-java-archive'
        - 'application/x-ms-shortcut'
        - 'application/x-msdos-program'
        - 'application/x-msdownload'
        - 'application/x-python-code'
        - 'application/x-sh'

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

Field	Kind	Values
`host`	ends_with	`.bid` `.by` `.cf` `.click` `.cm` `.ga` `.gq` `.ir` `.kp` `.loan` `.ml` `.mm` `.party` `.pw` `.ru` `.su` `.sy` `.tk` `.top` `.tv` `.ve` `.work` `.xyz`
`resp_mime_types`	eq	`application/vnd.microsoft.portable-executable` `application/x-bat` `application/x-dosexec` `application/x-elf` `application/x-iso9660-image` `application/x-java-archive` `application/x-ms-shortcut` `application/x-msdos-program` `application/x-msdownload` `application/x-python-code` `application/x-sh`
`uri`	ends_with	`.bat` `.bin` `.cmd` `.cpl` `.dll` `.dylib` `.elf` `.exe` `.hta` `.iso` `.jar` `.js` `.lnk` `.msi` `.pif` `.ps1` `.py` `.reg` `.scr` `.sh` `.so` `.vbs` `.wsf`

`j` / `k`	Scroll down / up
`d` / `u`	Half-page down / up
`gg` / `G`	Top / bottom
`h` / `l`	History back / forward
`f`	Follow link (`Shift` = new tab)
`/`	Focus search
`?`	Toggle this help
`↑` / `↓`	Navigate search results
`Enter`	Open highlighted result
`Esc`	Close results / dialog

`type:`	`events` / `rules` / `providers`
`vendor:`	`sigma` / `elastic` / `splunk` / `kusto` / `chronicle` (vendor name alone also works: `sigma:`, `kql:`, `secops:`…)
`tactic:`	TA-id, slug, or name: `credential_access`, `TA0006`
`technique:`	technique or sub-technique ID: `T1003`, `T1003.001` (alias `tech:`)
`severity:`	`critical` / `high` / `medium` / `low` / `informational` (alias `sev:`)
`risk_score`	Numeric comparison on the Elastic risk score (0 to 100): `risk_score>50`, `risk_score<=20`, `risk_score=99` (alias `risk`; Elastic rules only)
`stages:`	Rules with exactly N pipeline stages
`correlation:`	`single_event` / `sequence` / `alternatives` / `alternatives_cross_log` / `all_required` / `correlated`
`with:`	Co-occurrence event-id; stacks (`with:4624 with:4769`) to require all, while a comma list in one occurrence (`with:4624,4769`) is an either-or group. Implies multi-event
`like:`	Structural neighbors of a rule slug (equivalents + subsumption stricter / broader): `like:comsvcs_lsass_memory_dump-splunk-sysmon`
`groupby:`	Entity-grouping substring match against `group_by_keys`: `groupby:user`, `groupby:host`
`uses:`	Rules whose predicate tree touches the field (any kind, any value): `uses:CommandLine`
`excludes:`	Rules with top-level `not()` clauses on the field (FP whitelists): `excludes:ParentImage`
`field:` / `value:`	Predicate search; narrows rule cards to those with a matching leaf and drives the indicator tier. Unquoted = substring, wildcards allowed (`value:mimikatz`)
`indicator:`	Shorthand for `field:F value:V`: `indicator:Image=*\powershell.exe`
`kind:`	Filter by predicate kind. Narrows rule cards to those carrying a matching predicate leaf (`vendor:elastic kind:cidr_match`) and drives the indicator tier: `contains` / `starts_with` / `ends_with` / `regex` / `cidr` / `eq` / `in` … (operator aliases `op:`/`match:`)
`has:` / `no:`	`sample`, `field`, `notes`, `refs`, `trace`, `thirdparty`, `rule`, `pattern`, `timewindow`, `threshold`, `newterms`, `sigma`/`elastic`/`splunk`/`kusto`/`chronicle`
`-op:val`	Exclude matches; works on most operators but not `type:`/`like:`/`has:`/`no:` (use `no:<flag>` to exclude a rule flag): `tactic:execution -vendor:splunk`. Standalone `-kind:`/`-field:`/`-value:` drop every rule carrying a matching predicate leaf (`type:rules -kind:is_null`)
`field:"…"` / `value:"…"`	Quoted value = anchored exact match (also allows spaces): `value:"net user"`
`a,b`	Comma = OR inside one operator (`vendor:sigma,elastic`, `severity:high,critical`); repeating a facet merges the same way. `field:`/`value:` never split (literal commas)
`vendors:` / `stage:`	Singular and plural spellings fold to the canonical operator and value: `tactics:` = `tactic:`, `type:event` = `type:events`, `correlation:sequences` = `correlation:sequence`, `has:thresholds` = `has:threshold`
`"quoted phrase"`	Exact-match a multi-word phrase (free text)

HTTP Request to Low Reputation TLD or Suspicious File Extension

MITRE ATT&CK coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_suspicious_tld`

Stage 2: `selection_malicious_ext`

Stage 3: `selection_malicious_mime`

Indicators

Keyboard shortcuts

Search operators

HTTP Request to Low Reputation TLD or Suspicious File Extension

MITRE ATT&CK coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_suspicious_tld

Stage 2: selection_malicious_ext

Stage 3: selection_malicious_mime

Indicators

Stage 0: `condition`

Stage 1: `selection_suspicious_tld`

Stage 2: `selection_malicious_ext`

Stage 3: `selection_malicious_mime`