Cisco IOS XE VTY Access Class Tampering

Status: production
Severity: low
Group by: _time, dest
Author: Nasreddine Bencherchali
Source: github.com/splunk/security_content

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.

MITRE ATT&CK coverage

Tactic	Techniques
Stealth	`T1562` Impair Defenses
Lateral Movement	`T1021` Remote Services

Rule body splunk

name: Cisco IOS XE VTY Access Class Tampering
id: a01ca274-16cb-476d-a814-d2ffe29d8905
version: 1
creation_date: '2026-05-19'
modification_date: '2026-05-20'
author: Nasreddine Bencherchali
status: production
type: Anomaly
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.
data_source:
    - Cisco IOS Logs
search: |-
    `cisco_ios`
    facility IN ("HA_EM", "PARSER")
    mnemonic IN ("LOG", "CFGLOG_LOGGEDCMD")
    message_text IN (
        "*access-class*",
        "*configure http*",
        "*line vty*"
    )
    | rex field=message_text "^(?:[^:]+:\s+)?(?:catchall:\s+)?(?<eem_command>.+?)\s*$"
    | rex field=message_text "<enteredCommand><cli>(?<parser_command>.*?)</cli>"
    | rex field=message_text "<user>(?<parser_user>[^<]+)</user>"
    | rex field=message_text "<srcIP>(?<parser_src_ip>[^<]+)</srcIP>"
    | eval command=lower(trim(coalesce(parser_command, eem_command, "")))
    | eval event_type=case(
        like(command, "configure http%") OR like(command, "ip http secure-server%"), "http_config",
        like(command, "line vty%"), "line_vty",
        like(command, "no access-class%"), "remove_access_class",
        like(command, "access-class%"), "add_access_class",
        true(), null())
    | where isnotnull(event_type)
    | eval user=coalesce(parser_user, user, "unknown")
    | eval src_ip=coalesce(parser_src_ip, src_ip, "unknown")
    | eval dest=coalesce(host, dvc, dest, "unknown")
    | bin _time span=1m
    | stats count min(_time) as firstTime
                  max(_time) as lastTime
                  values(event_type) as event_types
                  values(user) as user
                  values(src_ip) as src_ip
                  values(command) as commands
      by _time dest
    | where mvfind(event_types, "line_vty") >= 0
            AND
            mvfind(event_types, "remove_access_class") >= 0
            AND
            mvfind(event_types, "add_access_class") >= 0
    | `security_content_ctime(firstTime)`
    | `security_content_ctime(lastTime)`
    | `cisco_ios_xe_vty_access_class_tampering_filter`
how_to_implement: |
    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.
references:
    - https://www.cisa.gov/news-events/cybersecurity-advisories/aa25-239a
    - https://blog.talosintelligence.com/salt-typhoon-analysis/
drilldown_searches:
    - name: View the detection results for - "$dest$"
      search: '%original_detection_search% | search  dest = "$dest$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$dest$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$dest$") | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
      earliest_offset: 7d
      latest_offset: "0"
intermediate_findings:
    entities:
        - field: dest
          type: system
          score: 20
          message: Cisco IOS-XE VTY access-class settings were removed and reapplied on $dest$ by $user$.
threat_objects:
    - field: commands
      type: command
analytic_story:
    - Salt Typhoon
asset_type: Network
mitre_attack_id:
    - T1562
    - T1021
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: application
security_domain: network
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/emerging_threats/SaltTyphoon/salttyphoon_cisco.log
          source: ctb:catalyst:syslog
          sourcetype: cisco:ios
      test_type: unit

Stages and Predicates

Stage 1: `search`

`cisco_ios`
facility IN ("HA_EM", "PARSER")
mnemonic IN ("LOG", "CFGLOG_LOGGEDCMD")
message_text IN (
    "*access-class*",
    "*configure http*",
    "*line vty*"
)

Stage 2: `rex`

| rex field=message_text "^(?:[^:]+:\s+)?(?:catchall:\s+)?(?<eem_command>.+?)\s*$"

Stage 3: `rex`

| rex field=message_text "<enteredCommand><cli>(?<parser_command>.*?)</cli>"

Stage 4: `rex`

| rex field=message_text "<user>(?<parser_user>[^<]+)</user>"

Stage 5: `rex`

| rex field=message_text "<srcIP>(?<parser_src_ip>[^<]+)</srcIP>"

Stage 6: `eval`

| eval command=lower(trim(coalesce(parser_command, eem_command, "")))

Stage 7: `eval`

| eval event_type=case(
    like(command, "configure http%") OR like(command, "ip http secure-server%"), "http_config",
    like(command, "line vty%"), "line_vty",
    like(command, "no access-class%"), "remove_access_class",
    like(command, "access-class%"), "add_access_class",
    true(), null())

event_type =

iflike(command, "configure http%") OR like(command, "ip http secure-server%")"http_config"

eliflike(command, "line vty%")"line_vty"

eliflike(command, "no access-class%")"remove_access_class"

eliflike(command, "access-class%")"add_access_class"

elsenull()

Stage 8: `where`

| where isnotnull(event_type)

Stage 9: `eval`

| eval user=coalesce(parser_user, user, "unknown")

Stage 10: `eval`

| eval src_ip=coalesce(parser_src_ip, src_ip, "unknown")

Stage 11: `eval`

| eval dest=coalesce(host, dvc, dest, "unknown")

Stage 12: `bucket`

| bin _time span=1m

Stage 13: `stats`

| stats count min(_time) as firstTime
              max(_time) as lastTime
              values(event_type) as event_types
              values(user) as user
              values(src_ip) as src_ip
              values(command) as commands
  by _time dest

Stage 14: `where`

| where mvfind(event_types, "line_vty") >= 0
        AND
        mvfind(event_types, "remove_access_class") >= 0
        AND
        mvfind(event_types, "add_access_class") >= 0

Stage 15: `search`

| `security_content_ctime(firstTime)`

Stage 16: `search`

| `security_content_ctime(lastTime)`

Stage 17: `search`

| `cisco_ios_xe_vty_access_class_tampering_filter`

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
`event_type`	is_not_null	(no value, null check)
`facility`	in	`"HA_EM"` `"PARSER"`
`message_text`	in	`"access-class"` `"configure http"` `"line vty"`
`mnemonic`	in	`"CFGLOG_LOGGEDCMD"` `"LOG"`
`sourcetype`	eq	`cisco:ios`

`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)

Cisco IOS XE VTY Access Class Tampering

MITRE ATT&CK coverage

Rule body splunk

Stages and Predicates

Stage 1: `search`

Stage 2: `rex`

Stage 3: `rex`

Stage 4: `rex`

Stage 5: `rex`

Stage 6: `eval`

Stage 7: `eval`

Stage 8: `where`

Stage 9: `eval`

Stage 10: `eval`

Stage 11: `eval`

Stage 12: `bucket`

Stage 13: `stats`

Stage 14: `where`

Stage 15: `search`

Stage 16: `search`

Stage 17: `search`

Indicators

Keyboard shortcuts

Search operators

Cisco IOS XE VTY Access Class Tampering

MITRE ATT&CK coverage

Rule body splunk

Stages and Predicates

Stage 1: search

Stage 2: rex

Stage 3: rex

Stage 4: rex

Stage 5: rex

Stage 6: eval

Stage 7: eval

Stage 8: where

Stage 9: eval

Stage 10: eval

Stage 11: eval

Stage 12: bucket

Stage 13: stats

Stage 14: where

Stage 15: search

Stage 16: search

Stage 17: search

Indicators

Stage 1: `search`

Stage 2: `rex`

Stage 3: `rex`

Stage 4: `rex`

Stage 5: `rex`

Stage 6: `eval`

Stage 7: `eval`

Stage 8: `where`

Stage 9: `eval`

Stage 10: `eval`

Stage 11: `eval`

Stage 12: `bucket`

Stage 13: `stats`

Stage 14: `where`

Stage 15: `search`

Stage 16: `search`

Stage 17: `search`