Detection: Cisco Secure Firewall - Citrix NetScaler Memory Overread Attempt

Updated Date: 2025-07-17 ID: 93db24a0-fd21-45d7-9daf-84afd5a8cca2 Author: Michael Haag, Nasreddine Bencherchali, Splunk, Talos NTDR Type: TTP Product: Splunk Enterprise Security

Description

This analytic detects exploitation activity of CVE-2025-5777 using Cisco Secure Firewall Intrusion Events. It leverages Cisco Secure Firewall Threat Defense IntrusionEvent logs to identify cases where Snort signature 65118 (Citrix NetScaler memory overread attempt) is triggered If confirmed malicious, this behavior is highly indicative of a potential exploitation of CVE-2025-5777.

Search

 1`cisco_secure_firewall` 
 2EventType=IntrusionEvent 
 3signature_id = 65118
 4
 5| fillnull
 6
 7| stats min(_time) as firstTime
 8        max(_time) as lastTime
 9        values(signature_id) as signature_id
10        values(signature) as signature
11        values(class_desc) as class_desc
12        values(MitreAttackGroups) as MitreAttackGroups
13        values(InlineResult) as InlineResult
14        values(InlineResultReason) as InlineResultReason
15        values(src_ip) as src_ip
16        values(dest_port) as dest_port
17        values(rule) as rule
18        values(transport) as transport
19        values(app) as app
20        by dest_ip
21
22| `security_content_ctime(firstTime)`
23
24| `security_content_ctime(lastTime)`
25
26| `cisco_secure_firewall___citrix_netscaler_memory_overread_attempt_filter`

Data Source

Name	Platform	Sourcetype	Source
Cisco Secure Firewall Threat Defense Intrusion Event	N/A	`'cisco:sfw:estreamer'`	`'not_applicable'`

Macros Used

Name	Value
cisco_secure_firewall	`sourcetype="cisco:sfw:estreamer"`
cisco_secure_firewall___citrix_netscaler_memory_overread_attempt_filter	`search *`

cisco_secure_firewall___citrix_netscaler_memory_overread_attempt_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK

+ Kill Chain Phases

+ NIST

+ CIS

- Threat Actors

ID	Technique	Tactic
T1203	Exploitation for Client Execution	Execution
T1059	Command and Scripting Interpreter	Execution

Installation

DE.CM

CIS 10

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting	Value
Disabled	true
Cron Schedule	`0 * * * *`
Earliest Time	`-70m@m`
Latest Time	`-10m@m`
Schedule Window	`auto`
Creates Notable	Yes
Rule Title	`%name%`
Rule Description	`%description%`
Notable Event Fields	user, dest
Creates Risk Event	True

This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

Implementation

This search requires Cisco Secure Firewall Threat Defense Logs, which includes the FileEvent EventType. This search uses an input macro named cisco_secure_firewall. We strongly recommend that you specify your environment-specific configurations (index, source, sourcetype, etc.) for Cisco Secure Firewall Threat Defense logs. Replace the macro definition with configurations for your Splunk environment. The search also uses a post-filter macro designed to filter out known false positives. The logs are to be ingested using the Splunk Add-on for Cisco Security Cloud (https://splunkbase.splunk.com/app/7404). The malware & file access policy must also enable logging.

Known False Positives

Security testing or vulnerability scanners might trigger this. Investigate any potential matches to determine if they're legitimate.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message:

Potential exploitation of CVE-2025-5777 from $src_ip$

Risk Object	Risk Object Type	Risk Score	Threat Objects
dest_ip	system	85	src_ip

References

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`not_applicable`	`cisco:sfw:estreamer`
Integration	✅ Passing	Dataset	`not_applicable`	`cisco:sfw:estreamer`

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

Source: GitHub | Version: 1