CVE-2025-20393 Google Chronicle · YARA-L

Detect CVE-2025-20393 — Cisco Multiple Products Improper Input Validation (KEV) in Google Chronicle

Detects exploitation attempts targeting CVE-2025-20393, an improper input validation vulnerability (CWE-20) affecting Cisco Multiple Products. This vulnerability is listed in CISA's Known Exploited Vulnerabilities catalog, indicating active in-the-wild exploitation. Attackers may leverage this flaw to bypass security controls, execute unauthorized commands, or gain elevated access to affected Cisco appliances.

MITRE ATT&CK

Tactic
Initial Access Privilege Escalation Lateral Movement

YARA-L Detection Query

Google Chronicle (YARA-L)
yaral 
rule cve_2025_20393_cisco_input_validation {
  meta:
    author = "df00tech"
    description = "Detects CVE-2025-20393 exploitation — Cisco improper input validation"
    severity = "HIGH"
    priority = "HIGH"
    reference = "https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-sma-attack-N9bf4"

  events:
    $e.metadata.event_type = "NETWORK_HTTP"
    $e.target.application = /(?i)cisco/
    (
      $e.network.http.request_url = /(\.\.\/|%2e%2e%2f|%252e|;|%00)/
      or $e.metadata.description = /(?i)(input validation|malformed|invalid input)/
    )
    $src_ip = $e.principal.ip

  match:
    $src_ip over 5m

  outcome:
    $event_count = count_distinct($e.metadata.id)
    $target_hosts = array_distinct($e.target.hostname)

  condition:
    #e > 2
}
high severity medium confidence

Chronicle YARA-L rule detecting repeated suspicious HTTP requests to Cisco products containing path traversal or input injection patterns from the same source IP within 5 minutes.

Data Sources

Chronicle network telemetryCisco UDM logs

Required Tables

network_http

False Positives & Tuning

  • Authorized red team exercises targeting Cisco infrastructure
  • Cisco Smart Software Manager or licensing services using encoded callback URLs
  • Third-party ITSM integrations with non-standard character handling in Cisco API requests

Other platforms for CVE-2025-20393

Microsoft Sentinel (KQL) Splunk (SPL) Elastic Security (Elastic) IBM QRadar (QRadar) Sumo Logic CSE (Sumo) CrowdStrike LogScale (LogScale) All platforms (combined) →

Testing Methodology

Validate this detection against 3 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.

  1. Test 1Path Traversal Probe Against Cisco SMA Interface

    Expected signal: HTTP request log entry with URI containing '../' sequences recorded in Cisco SMA access log; network flow record from test host to Cisco appliance on port 443

  2. Test 2Null Byte Injection Input Validation Test

    Expected signal: HTTP request containing '%00' in query string logged by network proxy or Cisco appliance; potential error response indicating input validation failure

  3. Test 3Automated Exploitation Pattern Simulation with Repeated Requests

    Expected signal: Ten sequential HTTP requests with encoded path traversal sequences from same source IP within 10 seconds, logged across Cisco access logs and network flow telemetry

Last updated: 2026-06-19 Research depth: standard
References (2)

Response Playbook

Triage

  1. Identify all Cisco products in the environment and cross-reference with the advisory at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-sma-attack-N9bf4 to determine if affected versions are deployed.
  2. Review firewall and proxy logs for the alerting source IP — determine if the source is internal (lateral movement indicator) or external (initial access attempt), and check for prior reconnaissance activity (port scans, enumeration) from the same IP.
  3. Inspect the specific request URI and payload that triggered the alert for signs of active exploitation (successful HTTP 200 responses, unusual response sizes, session token creation following the request).
  4. Check Cisco device authentication logs for any privilege escalation, new admin account creation, or configuration changes immediately following the suspicious requests.

Containment

  1. If exploitation is confirmed, immediately isolate the affected Cisco appliance from the network by applying ACLs or removing it from service, and revoke any administrative sessions active on the device.
  2. Block the attacker's source IP(s) at the perimeter firewall and web application firewall, and apply rate limiting or geo-blocking if the source geography is unexpected for your environment.

Evidence Collection

  1. Export full access logs, error logs, and audit logs from the affected Cisco appliance covering the 48-hour window around the first suspicious request, preserving timestamps and cryptographic integrity.
  2. Capture a running process list, active network connections (netstat/ss output), and current configuration snapshot from the affected device before any remediation actions to preserve forensic state.

Escalation Criteria

  • !Escalate immediately if HTTP responses to the malicious requests indicate successful exploitation (200 OK with unexpected content, session establishment, or configuration change confirmation messages).
  • !Escalate if lateral movement indicators are detected — e.g., the Cisco appliance initiating outbound connections to internal hosts or external C2 infrastructure following the initial exploitation attempt.

Investigation Guide

Related Techniques

[object Object][object Object][object Object]

Forensic Artifacts

  • >Cisco appliance HTTP access logs showing malformed or path-traversal requests with attacker source IPs
  • >System audit logs recording configuration changes, privilege escalations, or new account creation following suspicious requests
  • >Network flow records (NetFlow/IPFIX) capturing anomalous outbound connections from the Cisco appliance post-exploitation

Tuning Guidance

Reduce false positives by filtering known vulnerability scanner source IPs (Tenable, Qualys, Rapid7 NAT ranges) and Cisco's own Smart Licensing callback servers. Raise confidence threshold by correlating HTTP 200 response codes and anomalous response body sizes alongside the input pattern match. Consider tuning the minimum request count threshold based on your environment's normal Cisco management traffic volume — busy environments may need count > 10 rather than count > 1.

Hunting Queries

30-day retrospective hunt for repeated path traversal or null byte injection patterns against Cisco appliances, useful for identifying dwell time and initial compromise date.

Hunting — KQL
kql 
CommonSecurityLog
| where TimeGenerated >= ago(30d)
| where DeviceVendor == "Cisco"
| where RequestURL contains ".." or RequestURL contains "%2e" or RequestURL contains "%00"
| summarize count() by SourceIP, DestinationHostName, RequestURL
| where count_ > 5
| order by count_ desc
Hunting — SPL
spl 
index=cisco earliest=-30d
| eval suspicious=if(match(uri, "(\.\./|%2e%2e|%00)"), 1, 0)
| where suspicious=1
| stats count by src_ip, dest_host, uri
| where count > 5
| sort -count

Atomic Red Team Tests

Test 1 Path Traversal Probe Against Cisco SMA Interface
linux

Simulates an attacker probing a Cisco Secure Email and Web Manager (SMA) for the CVE-2025-20393 improper input validation vulnerability using path traversal sequences in the URI.

Command

bash 
curl -v -k 'https://TARGET_CISCO_IP/oem/admin/../../etc/passwd' -H 'User-Agent: Mozilla/5.0' --max-time 10 2>&1 | tee /tmp/cve_2025_20393_probe.log

Cleanup

bash 
rm -f /tmp/cve_2025_20393_probe.log

Expected Telemetry

HTTP request log entry with URI containing '../' sequences recorded in Cisco SMA access log; network flow record from test host to Cisco appliance on port 443

Expected Detection

Alert triggered by KQL/SPL query matching path traversal regex in RequestURL field for Cisco device vendor

Test 2 Null Byte Injection Input Validation Test
linux

Tests Cisco appliance handling of null byte injection in query parameters, a common CWE-20 exploitation vector that may bypass input validation filters.

Command

bash 
curl -v -k 'https://TARGET_CISCO_IP/cgi-bin/admin.pl?cmd=show%00version' -H 'User-Agent: Mozilla/5.0' --max-time 10 2>&1 | tee /tmp/nullbyte_test.log

Cleanup

bash 
rm -f /tmp/nullbyte_test.log

Expected Telemetry

HTTP request containing '%00' in query string logged by network proxy or Cisco appliance; potential error response indicating input validation failure

Expected Detection

SPL and KQL queries matching null byte (%00) pattern in URI against Cisco source log entries

Test 3 Automated Exploitation Pattern Simulation with Repeated Requests
linux

Simulates automated exploitation tool behavior by sending multiple malformed requests in rapid succession, triggering sequence-based and count-based detection logic.

Command

bash 
for i in $(seq 1 10); do curl -sk -o /dev/null -w "%{http_code}\n" 'https://TARGET_CISCO_IP/admin/%2e%2e/%2e%2e/etc/shadow' --max-time 5; sleep 0.5; done | tee /tmp/repeated_probe.log

Cleanup

bash 
rm -f /tmp/repeated_probe.log

Expected Telemetry

Ten sequential HTTP requests with encoded path traversal sequences from same source IP within 10 seconds, logged across Cisco access logs and network flow telemetry

Expected Detection

Sequence-based EQL and YARA-L rules triggering on count > 2 from same source IP within 5-minute window; Splunk aggregation query showing attempt_count > 1

Related Detections

Tactic Hubs

TA0001Initial AccessTA0004Privilege EscalationTA0008Lateral Movement

Related Techniques

T1190Exploit Public-Facing ApplicationT1078Valid AccountsT1210Exploitation of Remote Services

Same Tactic: Initial Access

Popular Detections