Compression DLL Loaded by Unusual Process

Status: production
Kind: building block (feeds higher-level correlation rules; not a standalone alert)
Severity: low
Time window: 119m
Author: Elastic
Source: github.com/elastic/detection-rules

Identifies the image load of a compression DLL. Adversaries will often compress and encrypt data in preparation for exfiltration.

MITRE ATT&CK coverage

Tactic	Techniques
Collection	`T1560.002` Archive Collected Data: Archive via Library

Event coverage

Provider	Event	Title
Sysmon	Event ID 7	Image loaded

Rule body elastic

[metadata]
creation_date = "2023/07/06"
integration = ["endpoint"]
maturity = "production"
updated_date = "2026/03/24"

[rule]
author = ["Elastic"]
building_block_type = "default"
description = """
Identifies the image load of a compression DLL. Adversaries will often compress and encrypt data in preparation for
exfiltration.
"""
from = "now-119m"
index = ["logs-endpoint.events.library-*"]
interval = "60m"
language = "eql"
license = "Elastic License v2"
name = "Compression DLL Loaded by Unusual Process"
risk_score = 21
rule_id = "d197478e-39f0-4347-a22f-ba654718b148"
severity = "low"
tags = [
    "Domain: Endpoint",
    "OS: Windows",
    "Use Case: Threat Detection",
    "Tactic: Collection",
    "Data Source: Elastic Defend",
    "Rule Type: BBR",
]
timestamp_override = "event.ingested"
type = "eql"

query = '''
library where host.os.type == "windows" and event.action == "load" and
  dll.name : ("System.IO.Compression.FileSystem.ni.dll", "System.IO.Compression.ni.dll") and
  not 
  (
    (
      process.executable : (
        "?:\\Program Files\\*",
        "?:\\Program Files (x86)\\*",
        "?:\\Windows\\Microsoft.NET\\Framework*\\mscorsvw.exe",
        "?:\\Windows\\System32\\sdiagnhost.exe",
        "?:\\Windows\\System32\\inetsrv\\w3wp.exe",
        "?:\\Windows\\SysWOW64\\inetsrv\\w3wp.exe",
        "?:\\ProgramData\\Microsoft\\Windows Defender Advanced Threat Protection\\DataCollection\\*\\OpenHandleCollector.exe"
      ) and process.code_signature.trusted == true
    ) or
    (
      process.name : "NuGet.exe" and process.code_signature.trusted == true and user.id : ("S-1-5-18", "S-1-5-20")
    )
  )
'''


[[rule.threat]]
framework = "MITRE ATT&CK"

[[rule.threat.technique]]
id = "T1560"
name = "Archive Collected Data"
reference = "https://attack.mitre.org/techniques/T1560/"

[[rule.threat.technique.subtechnique]]
id = "T1560.002"
name = "Archive via Library"
reference = "https://attack.mitre.org/techniques/T1560/002/"

[rule.threat.tactic]
id = "TA0009"
name = "Collection"
reference = "https://attack.mitre.org/tactics/TA0009/"

Stages and Predicates

Stage 1: `library`

library where host.os.type == "windows" and event.action == "load" and
  dll.name : ("System.IO.Compression.FileSystem.ni.dll", "System.IO.Compression.ni.dll") and
  not 
  (
    (
      process.executable : (
        "?:\\Program Files\\*",
        "?:\\Program Files (x86)\\*",
        "?:\\Windows\\Microsoft.NET\\Framework*\\mscorsvw.exe",
        "?:\\Windows\\System32\\sdiagnhost.exe",
        "?:\\Windows\\System32\\inetsrv\\w3wp.exe",
        "?:\\Windows\\SysWOW64\\inetsrv\\w3wp.exe",
        "?:\\ProgramData\\Microsoft\\Windows Defender Advanced Threat Protection\\DataCollection\\*\\OpenHandleCollector.exe"
      ) and process.code_signature.trusted == true
    ) or
    (
      process.name : "NuGet.exe" and process.code_signature.trusted == true and user.id : ("S-1-5-18", "S-1-5-20")
    )
  )

Exclusions

Top-level NOT(...) conjuncts: predicates this rule actively suppresses.

Field	Kind	Excluded values
`process.code_signature.trusted`	eq	`true`
`process.executable`	wildcard	`?:\Program Files\`, `?:\Program Files (x86)\`, `?:\Windows\Microsoft.NET\Framework\mscorsvw.exe`, `?:\Windows\System32\sdiagnhost.exe`, `?:\Windows\System32\inetsrv\w3wp.exe`, `?:\Windows\SysWOW64\inetsrv\w3wp.exe`, `?:\ProgramData\Microsoft\Windows Defender Advanced Threat Protection\DataCollection\\OpenHandleCollector.exe`
`process.code_signature.trusted`	eq	`true`
`process.name`	eq	`NuGet.exe`
`user.id`	eq	`S-1-5-18`, `S-1-5-20`

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
`dll.name`	wildcard	`System.IO.Compression.FileSystem.ni.dll` `System.IO.Compression.ni.dll`
`event.action`	eq	`load` corpus 9 (elastic 9)

`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)

Compression DLL Loaded by Unusual Process

MITRE ATT&CK coverage

Event coverage

Rule body elastic

Stages and Predicates

Stage 1: `library`

Exclusions

Indicators

Keyboard shortcuts

Search operators

Compression DLL Loaded by Unusual Process

MITRE ATT&CK coverage

Event coverage

Rule body elastic

Stages and Predicates

Stage 1: library

Exclusions

Indicators

Stage 1: `library`