Analysis Summary

Cisco has revealed a critical vulnerability in its IOS and IOS XE Software that could allow attackers to crash affected devices or gain complete control through remote code execution. The flaw, located in the Simple Network Management Protocol (SNMP) subsystem, arises from a stack overflow triggered by a specially crafted SNMP packet sent over IPv4 or IPv6 networks. Affecting all SNMP versions, this issue has already been exploited in real-world attacks, prompting urgent calls for network administrators to secure their systems. Cisco discovered the vulnerability during a Technical Assistance Center support case, with some exploitation cases linked to compromised local administrator credentials.

The vulnerability enables two major attack scenarios. A remote, low-privileged attacker with valid SNMPv2c read-only community strings or SNMPv3 credentials could launch a denial-of-service (DoS) attack, forcing devices to reload and disrupting operations. In more severe cases, a highly privileged attacker possessing administrative or level 15 access could execute arbitrary code as the root user on IOS XE systems, resulting in full device compromise. This broad impact extends across various Cisco routers, switches, and access points running vulnerable IOS or IOS XE versions with SNMP enabled. However, Cisco’s IOS XR and NX-OS platforms remain unaffected.

Given SNMP’s widespread use for network monitoring, the potential fallout is serious DoS attacks could paralyze key infrastructure, while remote code execution could lead to data theft, lateral movement, or malware installation. Many organizations remain at risk due to default SNMP configurations that inadvertently expose their devices. Cisco has stressed that no complete workaround exists, but certain mitigations can help reduce risk. Administrators are advised to restrict SNMP access to trusted IPs, disable vulnerable object IDs (OIDs) using the “snmp-server view” command, and regularly audit configurations with “show snmp host” or “show snmp user” commands. Meraki users should coordinate with Cisco support to apply similar restrictions.

Cisco has released patches through its September 2025 Semiannual Security Advisory Bundled Publication and urges immediate upgrades. Administrators can verify their device status and find fixed software versions using the Cisco Software Checker tool. In the absence of timely patching, attackers could exploit this vulnerability to gain root-level control or disrupt business-critical operations. The incident highlights the critical importance of SNMP hardening, credential management, and proactive patching to protect increasingly interconnected enterprise networks.

Impact

• Denial of Service
• Gain Access

Remediation

• Immediately upgrade to the fixed IOS or IOS XE versions released in Cisco’s September 2025 Semiannual Security Advisory Bundled Publication.
• Use the Cisco Software Checker tool to verify exposure and identify patched releases for your specific device models.
• Restrict SNMP access to trusted IP addresses or management networks only, limiting exposure to the internet or untrusted users.
• Disable vulnerable Object IDs (OIDs) using the snmp-server view command to create a restricted SNMP view, and apply it to SNMPv2c community strings or SNMPv3 groups.
• Regularly audit SNMP configurations using commands such as:
• show running-config | include snmp-server community (for SNMPv1/v2c)
• show snmp user (for SNMPv3)
• show snmp host (to verify host access)
• Remove default or unused community strings and enforce strong SNMPv3 authentication and encryption mechanisms.
• Limit SNMP privileges—u