Detect Citrix NetScaler Out-of-Bounds Read (CVE-2026-3055) in CrowdStrike LogScale
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
LogScale Detection Query
#event_simpleName=NetworkConnectIP4 OR #event_simpleName=NetworkReceiveAcceptIP4
| ComputerName = /netscaler|citrix|gateway/i OR RemotePort in (443, 80, 8443, 8080)
| HttpUri = /\/(vpn|citrix|logon|epa|rpc)\// AND (HttpUri = /\.\.\// OR HttpUri = /%00/ OR length(HttpUri) > 512)
| stats count(aid) as connection_count, dc(HttpUri) as unique_uris, min(timestamp) as first_seen, max(timestamp) as last_seen by RemoteAddressIP4, ComputerName
| where connection_count > 5
| sort -connection_countCrowdStrike Falcon LogScale (CQL) query detecting anomalous network connections to Citrix NetScaler endpoints with malformed URI patterns. Correlates connection frequency and URI diversity per source IP to identify CVE-2026-3055 exploitation probing.
Data Sources
Required Tables
False Positives & Tuning
- Falcon sensor-equipped hosts acting as reverse proxies or load balancers forwarding encoded traffic
- CrowdStrike threat graph enrichment processes generating synthetic network events for correlation
- Authorized red team operators using Falcon-monitored jump boxes to test NetScaler endpoints
- Network performance monitoring agents running continuous probes against gateway infrastructure
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.
Unlock Pro Content
Get the full detection package for CVE-2026-3055 including response playbook, investigation guide, and atomic red team tests.