ID | Technique | Tactic |
---|---|---|
T1587.002 | Code Signing Certificates | Resource Development |
T1588.004 | Digital Certificates | Resource Development |
T1071.001 | Web Protocols | Command And Control |
T1573.002 | Asymmetric Cryptography | Command And Control |
Detection: Cisco Secure Firewall - Blacklisted SSL Certificate Fingerprint
Description
The following analytic detects the use of known suspicious SSL certificates in any observed event where the SSL_CertFingerprint field is present. It leverages Cisco Secure Firewall logs and compares the SSL certificate SHA1 fingerprint against a blacklist of certificates associated with malware distribution, command and control (C2) infrastructure, or phishing campaigns. This activity is significant as adversaries often reuse or self-sign certificates across malicious infrastructure, allowing defenders to track and detect encrypted sessions even when domains or IPs change. If confirmed malicious, this may indicate beaconing, malware download, or data exfiltration over TLS/SSL.
Search
1`cisco_secure_firewall` EventType=* SSL_CertFingerprint=*
2
3| lookup sslbl_ssl_certificate_blacklist SHA1 as SSL_CertFingerprint OUTPUT Listingdate, Listingreason
4
5| where isnotnull(Listingreason)
6
7| stats min(_time) as firstTime max(_time) as lastTime
8 values(dest) as dest
9 values(dest_port) as dest_port
10 values(rule) as rule
11 values(url) as url
12 values(Listingreason) as Reasons
13 values(Listingdate) as "SSL Cert Listing Dates"
14 count by SSL_CertFingerprint src_ip transport action
15
16| `security_content_ctime(firstTime)`
17
18| `security_content_ctime(lastTime)`
19
20| `cisco_secure_firewall___blacklisted_ssl_certificate_fingerprint_filter`
Data Source
Name | Platform | Sourcetype | Source |
---|---|---|---|
Cisco Secure Firewall Threat Defense Connection Event | N/A | 'cisco:sfw:estreamer' |
'not_applicable' |
Macros Used
Name | Value |
---|---|
cisco_secure_firewall | sourcetype="cisco:sfw:estreamer" |
cisco_secure_firewall___blacklisted_ssl_certificate_fingerprint_filter | search * |
cisco_secure_firewall___blacklisted_ssl_certificate_fingerprint_filter
is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.
Annotations
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 |
Implementation
This search requires Cisco Secure Firewall Threat Defense Logs, which
includes the ConnectionEvent 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 access policy must also enable logging.
This search also make use of lookup based on https://sslbl.abuse.ch/blacklist/sslblacklist.csv. Make sure its available
Known False Positives
Certain SSL certificates may be flagged in threat intelligence feeds due to historical misuse, yet still be used by legitimate services, particularly in content delivery or shared hosting environments. Internal or self-signed certificates used in testing or development environments may inadvertently match known blacklisted fingerprints. It is recommended to validate the connection context (destination IP, domain, ClientApplication) and correlate with other indicators before taking action.
Associated Analytic Story
Risk Based Analytics (RBA)
Risk Message:
Suspicious SSL certificate fingerprint - [$SSL_CertFingerprint$] used in connections [ListingReason - $Reasons$] from $src_ip$
Risk Object | Risk Object Type | Risk Score | Threat Objects |
---|---|---|---|
src_ip | system | 20 | SSL_CertFingerprint, url |
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