Detect CVE-2026-20253: Splunk Enterprise Missing Authentication for Critical Function in Google Chronicle
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
YARA-L Detection Query
rule cve_2026_20253_splunk_unauth_access {
meta:
author = "df00tech Detection Engineering"
description = "Detects unauthenticated access to Splunk Enterprise critical API endpoints (CVE-2026-20253)"
severity = "CRITICAL"
priority = "HIGH"
reference = "https://advisory.splunk.com/advisories/SVD-2026-0603"
events:
$req.metadata.event_type = "NETWORK_HTTP"
$req.target.port in (8000, 8089, 9997)
(
re.regex($req.network.http.url, `/services/search/jobs`) or
re.regex($req.network.http.url, `/services/data/inputs`) or
re.regex($req.network.http.url, `/services/admin`) or
re.regex($req.network.http.url, `/services/authentication`) or
re.regex($req.network.http.url, `/en-US/splunkd/__raw/services`)
)
not re.regex($req.network.http.request_headers, `[Aa]uthorization: (Bearer|Splunk) `)
not re.regex($req.network.http.request_headers, `Cookie: .*splunkd_`)
$req.network.http.method in ("POST", "GET", "DELETE", "PUT")
condition:
$req
}Chronicle YARA-L rule detecting unauthenticated HTTP requests to Splunk Enterprise REST API paths on known Splunk ports, specifically checking for absence of Authorization and session cookie headers.
Data Sources
Required Tables
False Positives & Tuning
- Internal Splunk-to-Splunk communications using shared secret authentication not captured in standard headers
- API testing tools during authorized Splunk administration activities
- Splunk Universal Forwarder registration traffic on port 9997
- Network appliances with DPI that reclassify Splunk traffic headers
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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