Detect Citrix NetScaler Out-of-Bounds Read (CVE-2026-3055) in Sumo Logic CSE
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
Sumo Detection Query
_sourceCategory=citrix* OR _sourceCategory=netscaler* OR _sourceCategory=network/proxy
| parse regex "(?P<src_ip>\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})" nodrop
| parse regex "(?P<method>GET|POST|PUT|DELETE|OPTIONS|HEAD) (?P<uri_path>/[^\s]+)" nodrop
| where uri_path matches "/vpn/*" or uri_path matches "/citrix/*" or uri_path matches "/logon/*" or uri_path matches "/epa/*"
| where length(uri_path) > 512 or uri_path matches "*../*" or uri_path matches "*%00*"
| timeslice 5m
| stats count as request_count, dcount(uri_path) as unique_paths by src_ip, _timeslice
| where request_count > 10
| sort by request_count descSumo Logic query detecting high-frequency or malformed requests to Citrix NetScaler VPN and gateway paths. Parses raw syslog and proxy logs to identify source IPs submitting anomalous URI patterns associated with CVE-2026-3055 out-of-bounds read exploitation.
Data Sources
Required Tables
False Positives & Tuning
- Automated web application testing frameworks generating large payloads during QA cycles
- API integration partners sending complex encoded parameters through NetScaler gateway
- Content delivery networks forwarding encoded URLs that appear malformed in logs
- Security information aggregation tools consolidating logs with long metadata strings
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.