Detect CVE-2026-20253: Splunk Enterprise Missing Authentication for Critical Function in Splunk
Detects exploitation attempts targeting CVE-2026-20253, a missing authentication vulnerability (CWE-306) in Splunk Enterprise. This KEV-listed vulnerability allows unauthenticated access to critical Splunk functions. Attackers may leverage this to execute searches, exfiltrate data, or manipulate Splunk configurations without valid credentials.
MITRE ATT&CK
- Tactic
- Initial Access Persistence Collection
SPL Detection Query
index=proxy OR index=web OR index=splunk_audit
(uri_path="/services/search/jobs" OR uri_path="/services/data/inputs" OR uri_path="/services/admin*" OR uri_path="/services/authentication*" OR uri_path="/en-US/splunkd/__raw/services*")
NOT (auth_token=* OR http_user_agent="Splunk*" AND cookie=*)
| eval unauthenticated=if(isnull(username) OR username="-" OR username="", "true", "false")
| where unauthenticated="true"
| eval request_method=upper(method)
| where request_method IN ("POST", "GET", "DELETE", "PUT")
| stats count min(_time) as first_seen max(_time) as last_seen values(uri_path) as paths values(src_ip) as source_ips by dest_ip, dest_port
| where count > 1
| eval first_seen=strftime(first_seen, "%Y-%m-%dT%H:%M:%SZ"), last_seen=strftime(last_seen, "%Y-%m-%dT%H:%M:%SZ")
| sort -countIdentifies unauthenticated requests to Splunk Enterprise REST API endpoints from proxy or web logs. Aggregates by destination to surface repeated exploitation attempts.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Automated monitoring tools performing unauthenticated health checks against Splunk
- Misconfigured Splunk forwarders attempting registration without proper tokens
- Internal vulnerability scanners probing Splunk REST API endpoints
- Legacy integrations not yet migrated to token-based authentication
Other platforms for CVE-2026-20253
Testing Methodology
Validate this detection against 4 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.
- Test 1Unauthenticated Splunk Search Job Creation via REST API
Expected signal: HTTP POST to port 8089 without Authorization header; Splunk web_access.log entry with null/anonymous user; network flow record to TCP/8089
- Test 2Unauthenticated Splunk User Enumeration via REST API
Expected signal: HTTP GET to /services/authentication/users on port 8089 without credentials; response body containing user list if vulnerable
- Test 3Unauthenticated Splunk Index Listing and Data Access
Expected signal: Sequential unauthenticated GET and POST requests to Splunk REST API; multiple different /services/ paths accessed from same source IP within short timeframe
- Test 4Unauthenticated Splunk Configuration Modification Attempt
Expected signal: HTTP POST to /services/data/inputs/ without Authorization header; Splunk audit log entry for configuration change with anonymous user context
References (4)
- https://advisory.splunk.com/advisories/SVD-2026-0603
- https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk
- https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk
- https://nvd.nist.gov/vuln/detail/CVE-2026-20253
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