Detect CVE-2026-20253: Splunk Enterprise Missing Authentication for Critical Function in Sumo Logic CSE
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
Sumo Detection Query
_sourceCategory=*proxy* OR _sourceCategory=*web* OR _sourceCategory=*splunk*
| parse "* * * *" as src_ip, method, uri, status
| where uri matches "/services/search/jobs*" or uri matches "/services/data/inputs*" or uri matches "/services/admin*" or uri matches "/services/authentication*" or uri matches "/en-US/splunkd/__raw/services*"
| where !(uri matches "*splunkd_*") and !(uri matches "*auth_token*")
| where method in ("POST", "GET", "DELETE", "PUT")
| count by src_ip, uri, method, status
| where _count > 1
| sort by _count desc
| fields src_ip, uri, method, status, _countSumo Logic query detecting unauthenticated access attempts to Splunk Enterprise critical REST API endpoints, filtering for requests without authentication indicators.
Data Sources
Required Tables
False Positives & Tuning
- Automated API clients with authentication passed as query parameters rather than headers
- Monitoring agents configured without Splunk authentication credentials
- CDN or WAF intermediaries that strip authentication headers before logging
- OAuth flows using non-standard authentication paths that match URI patterns
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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