UNC4841 - Barracuda ESG Exploitation Indicators

Status: test
Severity: high
Log source: product linux, category file_event
Author: Nasreddine Bencherchali (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects file indicators as seen used by UNC4841 during their Barracuda ESG zero day exploitation.

MITRE ATT&CK coverage

Tactic	Techniques
Execution	No specific technique
Persistence	No specific technique
Stealth	No specific technique

Event coverage

Provider	Event
Sysmon-for-Linux	Event ID 11

Rule body yaml

title: UNC4841 - Barracuda ESG Exploitation Indicators
id: 5627c337-a9b2-407a-a82d-5fd97035ff39
status: test
description: Detects file indicators as seen used by UNC4841 during their Barracuda ESG zero day exploitation.
references:
    - https://www.mandiant.com/resources/blog/barracuda-esg-exploited-globally
author: Nasreddine Bencherchali (Nextron Systems)
date: 2023-06-16
modified: 2025-08-19
tags:
    - attack.execution
    - attack.persistence
    - detection.emerging-threats
    - attack.stealth
logsource:
    product: linux
    category: file_event
detection:
    selection:
        TargetFilename|endswith:
            - '/11111.tar'
            - '/aacore.sh'
            - '/appcheck.sh'
            - '/autoins'
            - '/BarracudaMailService'
            - '/etc/cron.daily/core_check.sh'
            - '/etc/cron.daily/core.sh'
            - '/etc/cron.hourly/aacore.sh'
            - '/etc/cron.hourly/appcheck.sh'
            - '/etc/cron.hourly/core.sh'
            - '/get_fs_info.pl'
            - '/imgdata.jpg'
            - '/install_att_v2.tar'
            - '/install_bvp74_auth.tar'
            - '/install_helo.tar'
            - '/install_reuse.tar'
            - '/intent_helo'
            - '/intent_reuse'
            - '/intentbas'
            # - '/mknod'
            - '/mod_attachment.lua'
            - '/mod_content.lua'
            - '/mod_require_helo.lua'
            - '/mod_rtf'
            - '/mod_sender.lua'
            - '/mod_udp.so'
            - '/nfsd_stub.ko'
            - '/resize_reisertab'
            - '/resize_risertab'
            - '/resize2fstab'
            - '/rverify'
            - '/saslautchd'
            - '/sendscd'
            - '/snapshot.tar'
            - '/tmp/p'
            - '/tmp/p7'
            - '/tmp/t'
            - '/update_v2.sh'
            - '/update_v31.sh'
            - '/update_v35.sh'
            - '/update_version'
    condition: selection
falsepositives:
    - Unlikely
level: high

Stages and Predicates

Stage 0: `condition`

selection

Stage 1: `selection`

selection:
    TargetFilename|endswith:
        - '/11111.tar'
        - '/aacore.sh'
        - '/appcheck.sh'
        - '/autoins'
        - '/BarracudaMailService'
        - '/etc/cron.daily/core_check.sh'
        - '/etc/cron.daily/core.sh'
        - '/etc/cron.hourly/aacore.sh'
        - '/etc/cron.hourly/appcheck.sh'
        - '/etc/cron.hourly/core.sh'
        - '/get_fs_info.pl'
        - '/imgdata.jpg'
        - '/install_att_v2.tar'
        - '/install_bvp74_auth.tar'
        - '/install_helo.tar'
        - '/install_reuse.tar'
        - '/intent_helo'
        - '/intent_reuse'
        - '/intentbas'
        - '/mod_attachment.lua'
        - '/mod_content.lua'
        - '/mod_require_helo.lua'
        - '/mod_rtf'
        - '/mod_sender.lua'
        - '/mod_udp.so'
        - '/nfsd_stub.ko'
        - '/resize_reisertab'
        - '/resize_risertab'
        - '/resize2fstab'
        - '/rverify'
        - '/saslautchd'
        - '/sendscd'
        - '/snapshot.tar'
        - '/tmp/p'
        - '/tmp/p7'
        - '/tmp/t'
        - '/update_v2.sh'
        - '/update_v31.sh'
        - '/update_v35.sh'
        - '/update_version'

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
`TargetFilename`	ends_with	`/11111.tar` `/BarracudaMailService` `/aacore.sh` `/appcheck.sh` `/autoins` `/etc/cron.daily/core.sh` `/etc/cron.daily/core_check.sh` `/etc/cron.hourly/aacore.sh` `/etc/cron.hourly/appcheck.sh` `/etc/cron.hourly/core.sh` `/get_fs_info.pl` `/imgdata.jpg` `/install_att_v2.tar` `/install_bvp74_auth.tar` `/install_helo.tar` `/install_reuse.tar` `/intent_helo` `/intent_reuse` `/intentbas` `/mod_attachment.lua` `/mod_content.lua` `/mod_require_helo.lua` `/mod_rtf` `/mod_sender.lua` `/mod_udp.so` `/nfsd_stub.ko` `/resize2fstab` `/resize_reisertab` `/resize_risertab` `/rverify` `/saslautchd` `/sendscd` `/snapshot.tar` `/tmp/p` `/tmp/p7` `/tmp/t` `/update_v2.sh` `/update_v31.sh` `/update_v35.sh` `/update_version`

`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)

UNC4841 - Barracuda ESG Exploitation Indicators

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection`

Indicators

Keyboard shortcuts

Search operators

UNC4841 - Barracuda ESG Exploitation Indicators

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection

Indicators

Stage 0: `condition`

Stage 1: `selection`