Cisco recently disclosed a highly critical zero-day vulnerability, CVE-2025-20352, impacting its widely deployed IOS and IOS XE software platforms. This flaw, which resides in the Simple Network Management Protocol (SNMP) subsystem, is being actively exploited in the wild, posing substantial risks to enterprise and service provider infrastructure.
What Is CVE-2025-20352?
This vulnerability stems from a stack overflow condition in the SNMP handler within affected Cisco devices. An attacker with network access and the ability to authenticate via SNMP (even with limited read-only privileges) can exploit this flaw by sending maliciously crafted SNMP packets. The consequences vary based on attacker privileges:
- Low-privileged attackers (with SNMPv2c read-only community strings or similar) can induce denial-of-service (DoS) conditions, causing device reloads.
- High-privileged attackers with elevated SNMP credentials (e.g., read-write access or SNMPv3 with privilege level 15) can achieve remote code execution, gaining full control over the device.
This allows not only system disruption but potentially persistent and stealthy compromise of mission-critical network gear.
Who and What Is Affected?
- All versions of Cisco IOS and IOS XE that have SNMP enabled and handle SNMP object identifiers without mitigations are impacted.
- Notable affected devices include Cisco Catalyst 9300 switches and Meraki MS390 when running vulnerable software versions.
- Cisco IOS XR and NX-OS platforms are not known to be vulnerable.
Real-World Threats and Exploitation
Cisco confirmed that CVE-2025-20352 is actively exploited, often tied to attackers obtaining administrator credentials via secondary means, then leveraging SNMP to escalate control. This attack vector is especially dangerous because it requires limited access yet can lead to full device compromise.
How to Protect Your Network
- Patch Immediately: Cisco has released updates in IOS XE 17.15.4a and other maintenance releases that address this critical vulnerability. Network operators should prioritize upgrading impacted devices.
- Restrict SNMP Access: Limit SNMP queries to trusted hosts only and use strong authentication and encryption for SNMPv3.
- Monitor and Audit: Keep an eye on SNMP logs and monitor for unusual SNMP traffic or configuration changes.
- Disable Vulnerable SNMP OIDs: When patches cannot be applied immediately, disabling certain SNMP object identifiers linked to the vulnerability can reduce exploitation risk—though this may impact management functionality.
Conclusion
CVE-2025-20352 is a stark reminder of the critical attack surface network management protocols represent in modern infrastructures. With active exploitation underway, organizations running Cisco IOS and IOS XE devices must act urgently to patch, restrict, and monitor SNMP usage to thwart potential network outages and breaches.
Staying vigilant and proactive with patch management and access controls is the line of defense against attackers exploiting such powerful vulnerabilities. This incident highlights the continuous importance of robust network security hygiene and timely vulnerability response.
For those managing Cisco networks, immediate action on this critical SNMP vulnerability is a must to safeguard against potential attacks disrupting operations or compromising sensitive data.
