Detect Fortinet Multiple Products Improper Verification of Cryptographic Signature (CVE-2025-59718) in Sumo Logic CSE
Detects exploitation of CVE-2025-59718, an improper verification of cryptographic signature vulnerability (CWE-347) affecting multiple Fortinet products. This vulnerability, listed in CISA's Known Exploited Vulnerabilities catalog, allows attackers to bypass signature validation checks, potentially enabling unsigned firmware/software installation, man-in-the-middle attacks on update channels, or code execution with elevated privileges on affected Fortinet appliances.
MITRE ATT&CK
Sumo Detection Query
_sourceCategory=network/fortinet OR _sourceCategory=security/fortigate
| where vendor = "Fortinet" or _sourceName matches "*fortigate*" or _sourceName matches "*fortios*"
| where (
message matches "*signature*fail*"
or message matches "*unsigned firmware*"
or message matches "*certificate verification failed*"
or message matches "*bypass*sig*"
or (subtype = "update" and status != "success")
)
| parse field=message "type=* subtype=* level=* vd=* eventtime=* logdesc=*" as event_type, event_subtype, log_level, vdom, event_time, log_desc nodrop
| if (message matches "*bypass*", 90, if (message matches "*unsigned*", 85, if (message matches "*signature*fail*", 80, 60))) as risk_score
| count by _sourceHost, _collector, event_type, event_subtype, log_desc, risk_score
| sort by risk_score descSearches Sumo Logic for Fortinet log events indicating cryptographic signature bypass or verification failures consistent with CVE-2025-59718 exploitation.
Data Sources
Required Tables
False Positives & Tuning
- Development or lab Fortinet instances with debug logging enabled
- MSSP environments where multiple Fortinet tenants generate expected validation noise
- Fortinet appliances undergoing legitimate vendor-assisted maintenance generating signature-related events
Other platforms for CVE-2025-59718
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 Fortinet Firmware Signature Bypass via Invalid Update Request
Expected signal: HTTP 400 or 403 response from Fortinet API with error body referencing signature validation failure; corresponding event in Fortinet system logs with type=event subtype=update level=alert
- Test 2Fortinet Management Interface Signature-Related Error Log Injection Test
Expected signal: Three syslog events appearing in SIEM with Fortinet device name, event type 'update' or 'system', and messages containing 'signature verification failed', 'cert verification failed', and 'unsigned firmware'
- Test 3Network-Level Simulation of Fortinet Update Channel Interception
Expected signal: Network flow logs showing Fortinet appliance connecting to update server via proxy; Fortinet logs showing certificate validation errors or signature failures when intercepted responses are presented
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