Critical Cisco SNMP Flaw Exploited: Root Access at Risk

Cisco SNMP Zero-Day CVE-2025-20352: Root Access and DoS Exploits in IOS and IOS XE

Summary

A critical zero-day vulnerability, tracked as CVE-2025-20352, has been discovered in the SNMP subsystem of Cisco IOS and IOS XE software. Actively exploited in the wild, this stack-based buffer overflow flaw enables attackers to crash affected devices or gain root-level access, leading to full system compromise. Devices running unpatched versions are at severe risk, especially if SNMP is exposed to untrusted networks. Cisco has released fixed software, making immediate upgrades essential.

Vulnerability Details

The flaw resides in the SNMP subsystem of Cisco IOS and IOS XE:

• Attack Vector: Exploitable remotely by attackers with SNMPv2c read-only community strings or valid SNMPv3 credentials.

• Impact:

  • Low-privileged attackers can trigger denial-of-service (DoS) by forcing device reloads.

  • High-privileged attackers can exploit the buffer overflow to execute arbitrary code with root-level privileges, gaining total control.

• Exploitation Method: Active campaigns exploit compromised administrator credentials first, then leverage the SNMP flaw for escalation.

• Affected Products: Cisco IOS, IOS XE, Meraki MS390 switches (CS 17 and earlier), and Cisco Catalyst 9300 series switches (CS 17 and earlier).

• CWE Reference: CWE-121 (Stack-based Buffer Overflow).

Cisco confirms no complete workaround exists. Only upgrading to fixed software fully eliminates the risk. Temporary mitigations, like restricting SNMP, disabling affected OIDs, and monitoring traffic, may help but can disrupt management functions.

Recommendations

• Immediate Patching: Upgrade to Cisco’s fixed IOS and IOS XE releases. This is the only reliable protection.

• Restrict SNMP Access: Limit SNMP exposure to trusted networks and users. Use the show snmp host command to monitor activity.

• Disable Vulnerable OIDs: Apply the snmp-server view command to disable risky OIDs (with caution as this may disrupt inventory and discovery).

• Assume Potential Compromise: Audit administrative accounts, rotate credentials, and review access logs to detect possible privilege abuse.

• Strengthen Vulnerability Management: Maintain a software inventory, ensure continuous patching, and validate vendor security practices.

MITRE ATT&CK TTPs

• TA0042 – Resource Development: T1588 (Obtain Capabilities), T1588.006 (Exploit Vulnerabilities)

• TA0001 – Initial Access: T1078 (Valid Accounts)

• TA0002 – Execution: T1059 (Command and Scripting Interpreter)

• TA0004 – Privilege Escalation: T1068 (Exploitation for Privilege Escalation)

• TA0040 – Impact: T1499 (Endpoint Denial of Service)

References

• Cisco Security Advisory – SNMP Vulnerability in IOS and IOS XE

• MITRE ATT&CK – Techniques & Tactics