Detection: Cisco IOS XE VTY Access Class Tampering

Updated Date: 2026-05-20 ID: a01ca274-16cb-476d-a814-d2ffe29d8905 Author: Nasreddine Bencherchali Type: Anomaly Product: Splunk Enterprise Security

Description

This analytic detects rapid modification of Cisco IOS-XE VTY access-class settings. The Salt Typhoon notes describe configure HTTP activity followed by line vty changes and removal/re-application of an access-class within 60 seconds.

Search

 1`cisco_ios`
 2facility IN ("HA_EM", "PARSER")
 3mnemonic IN ("LOG", "CFGLOG_LOGGEDCMD")
 4message_text IN (
 5    "*access-class*",
 6    "*configure http*",
 7    "*line vty*"
 8)
 9
10| rex field=message_text "^(?:[^:]+:\s+)?(?:catchall:\s+)?(?<eem_command>.+?)\s*$"
11
12| rex field=message_text "<enteredCommand><cli>(?<parser_command>.*?)</cli>"
13
14| rex field=message_text "<user>(?<parser_user>[^<]+)</user>"
15
16| rex field=message_text "<srcIP>(?<parser_src_ip>[^<]+)</srcIP>"
17
18| eval command=lower(trim(coalesce(parser_command, eem_command, "")))
19
20| eval event_type=case(
21    like(command, "configure http%") OR like(command, "ip http secure-server%"), "http_config",
22    like(command, "line vty%"), "line_vty",
23    like(command, "no access-class%"), "remove_access_class",
24    like(command, "access-class%"), "add_access_class",
25    true(), null())
26
27| where isnotnull(event_type)
28
29| eval user=coalesce(parser_user, user, "unknown")
30
31| eval src_ip=coalesce(parser_src_ip, src_ip, "unknown")
32
33| eval dest=coalesce(host, dvc, dest, "unknown")
34
35| bin _time span=1m
36
37| stats count min(_time) as firstTime
38              max(_time) as lastTime
39              values(event_type) as event_types
40              values(user) as user
41              values(src_ip) as src_ip
42              values(command) as commands
43  by _time dest
44
45| where mvfind(event_types, "line_vty") >= 0
46        AND
47        mvfind(event_types, "remove_access_class") >= 0
48        AND
49        mvfind(event_types, "add_access_class") >= 0
50
51| `security_content_ctime(firstTime)`
52
53| `security_content_ctime(lastTime)`
54
55| `cisco_ios_xe_vty_access_class_tampering_filter`

Data Source

Name	Platform	Sourcetype	Source
Cisco IOS Logs	Other	`'cisco:ios'`	`'cisco:ios'`

Macros Used

Name	Value
security_content_ctime	`convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)`
cisco_ios_xe_vty_access_class_tampering_filter	`search *`

cisco_ios_xe_vty_access_class_tampering_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK

+ Kill Chain Phases

+ NIST

+ CIS

- Threat Actors

ID	Technique	Tactic
T1021	Remote Services	Lateral Movement
T1562	Impair Defenses	Stealth

Exploitation

DE.AE

CIS 13

Ember Bear

Wizard Spider

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting	Value
Disabled	true
Cron Schedule	`0 * * * *`
Earliest Time	`-70m@m`
Latest Time	`-10m@m`
Schedule Window	`auto`
Creates Finding (Notable)	No
Creates Intermediate Finding (Risk Event)	Yes

Anomaly detections generate Intermediate Findings (Risk Events). They do not generate a Finding (Notable) directly.

Implementation

Use the Cisco Catalyst Add-on for Splunk (https://splunkbase.splunk.com/app/7538) to Ingest Cisco IOS-XE syslog with sourcetype "cisco:ios" and enable archive/config command logging.

Known False Positives

VTY ACL changes occur during legitimate management access updates. Filter approved maintenance windows and known administrators.

Associated Analytic Story

Salt Typhoon

Intermediate Findings

Message	Entity Field	Entity Type	Risk Score
Cisco IOS-XE VTY access-class settings were removed and reapplied on $dest$ by $user$.	dest	system	20

Threat Objects

Field	Type
commands	command

References

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`ctb:catalyst:syslog`	`cisco:ios`
Integration	✅ Passing	Dataset	`ctb:catalyst:syslog`	`cisco:ios`

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

Source: GitHub |

Version: 1