Detect Citrix NetScaler Out-of-Bounds Read (CVE-2026-3055) in IBM QRadar
Detects exploitation attempts targeting CVE-2026-3055, an out-of-bounds read vulnerability (CWE-125) in Citrix NetScaler ADC and NetScaler Gateway. This vulnerability is actively exploited in the wild (CISA KEV) and may allow unauthenticated remote attackers to read sensitive memory contents, potentially leading to information disclosure or enabling further attacks. Detection focuses on anomalous HTTP request patterns, NetScaler management plane access, and memory-related crash indicators.
MITRE ATT&CK
QRadar Detection Query
SELECT sourceip, destinationip, destinationport, URL, "Event Count", MIN(starttime) AS first_seen, MAX(starttime) AS last_seen
FROM events
WHERE LOGSOURCETYPENAME(devicetype) IN ('Citrix NetScaler', 'Citrix Access Gateway', 'Apache HTTP Server')
AND (URL LIKE '%/vpn/%' OR URL LIKE '%/citrix/%' OR URL LIKE '%/logon/%' OR URL LIKE '%/epa/%')
AND (LENGTH(URL) > 512 OR URL LIKE '%../%' OR URL LIKE '%00%' OR URL LIKE '%2e2e%')
AND starttime > NOW() - 7 DAYS
GROUP BY sourceip, destinationip, destinationport, URL
HAVING "Event Count" > 3
ORDER BY "Event Count" DESC
LAST 7 DAYSQRadar AQL query identifying suspicious HTTP requests to Citrix NetScaler management and VPN endpoints with anomalous URL patterns including excessive length, path traversal sequences, or null bytes indicative of CVE-2026-3055 exploitation.
Data Sources
Required Tables
False Positives & Tuning
- Vulnerability management platforms conducting authorized scans of NetScaler infrastructure
- Web crawlers or bots indexing publicly accessible Citrix gateway login pages
- Legitimate users with long session tokens or OAuth parameters in gateway URLs
- Internal monitoring tools polling NetScaler health endpoints with extended parameters
Other platforms for CVE-2026-3055
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.
- Test 1Simulate CVE-2026-3055 OOB Read Probe via Malformed VPN Endpoint Request
Expected signal: NetScaler access logs showing requests to /vpn/ with URI length >600 characters and path traversal sequences. HTTP response codes 400, 404, or 500 depending on patch status. Network capture showing outbound TCP connection to NetScaler port 443 with anomalous URI in HTTP request.
- Test 2Null Byte Injection Against NetScaler Gateway Authentication Endpoint
Expected signal: 15 sequential POST requests to /cgi/login from single source IP within 15 seconds. Varying response sizes across requests if OOB read is triggerable. NetScaler AppFW violation logs for null byte detection if AppFW is enabled. Process monitoring showing nsppe or nsnetsvc CPU spikes.
- Test 3Response Size Anomaly Validation for OOB Memory Disclosure
Expected signal: Two HTTP requests from same source IP — one to /vpn/index.html (baseline) and one to /epa/ with encoded path traversal. If vulnerable, probe response will be larger than baseline or contain unexpected binary content. NetScaler logs show both requests with response sizes in bytes_out field.
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