Detect CVE-2026-20253: Splunk Enterprise Missing Authentication for Critical Function in Microsoft Sentinel
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
KQL Detection Query
union isfuzzy=true
(
CommonSecurityLog
| where DeviceVendor =~ "Splunk"
| where RequestURL has_any ("/services/search/jobs", "/services/data/inputs", "/services/admin", "/services/authentication", "/en-US/splunkd/__raw/services")
| where isempty(AdditionalExtensions) or AdditionalExtensions !has "authToken"
| where RequestMethod in ("POST", "GET", "DELETE")
| project TimeGenerated, SourceIP, DestinationIP, RequestURL, RequestMethod, DeviceVendor, DeviceProduct, EventOutcome
),
(
W3CIISLog
| where csUriStem has_any ("/services/search/jobs", "/services/data/inputs", "/services/admin", "/services/authentication")
| where isempty(csUsername) or csUsername == "-"
| where csMethod in ("POST", "GET", "DELETE")
| project TimeGenerated, cIP, csUriStem, csMethod, scStatus, csUsername
)
| where TimeGenerated > ago(24h)Detects unauthenticated HTTP requests to sensitive Splunk Enterprise API endpoints that require authentication. Looks for requests lacking authentication tokens/usernames to critical Splunk service paths.
Data Sources
Required Tables
False Positives & Tuning
- Health check probes or monitoring agents that hit Splunk endpoints without credentials
- Internal network scanners performing asset inventory against Splunk ports
- Splunk forwarder registration traffic that may appear unauthenticated in some log parsers
- Load balancer or reverse proxy health checks targeting Splunk REST API paths
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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