CVE-2025-20352: Cisco IOS and IOS XE Software SNMP Denial of Service and Remote Code Execution Vulnerability

CVE-2025-20352 is a stack-based buffer overflow in the SNMP subsystem of Cisco IOS and IOS XE Software. It can let an attacker crash the device (denial of service) or, under higher privilege, run code as root and take full control. Network devices running these operating systems are common choke points for traffic and management; a successful attack can disrupt operations or give an adversary a foothold deep inside the infrastructure. Confirm exact impact and fixed releases against the official Cisco advisory.

How it works

The weakness is CWE-121: a stack-based buffer overflow. The SNMP process fails to properly bound-check certain input, so carefully crafted SNMP messages can overwrite memory on the stack. According to the CISA summary, a low-privileged attacker who can reach the SNMP service may force a reload and produce a denial-of-service condition. A high-privileged attacker may instead achieve remote code execution as the root user, obtaining complete control of the device. No public exploit mechanics beyond this class description are supplied here; treat any claimed payload or trigger as unverified until the vendor advisory is reviewed.

Am I affected? How to find it in your systems

Cisco IOS and IOS XE typically run on enterprise routers, switches, wireless controllers, and some security appliances. Inventory every device that presents an SNMP interface (UDP 161/162 or any non-default ports you have configured). Use your configuration-management database, network discovery tools, or CLI commands such as “show version” and “show snmp” to list running images and SNMP status. Compare the installed software train against the versions Cisco lists as vulnerable in its advisory; do not rely on third-party version tables. Also note whether SNMP community strings, SNMPv3 users, or access-control lists are present—any reachable SNMP listener is in scope until proven otherwise.

For signs of exploitation, watch for unexpected device reloads, SNMP-related process crashes, or anomalous SNMP traffic volumes in NetFlow, syslogs, or packet captures. Because the overflow can be triggered by a single crafted packet, absence of noisy scanning does not prove safety. Correlate any crash dumps or core files with the SNMP subsystem if your logging level permits.

How to remediate

Apply the vendor-supplied software update that addresses CVE-2025-20352 as soon as operational testing allows. Follow Cisco’s published upgrade path for your hardware and feature set; partial or interim images may not fully close the issue. After patching, re-verify SNMP configuration and remove any temporary work-arounds that are no longer needed. CISA’s required action is to apply mitigations per vendor instructions, follow BOD 22-01 guidance where cloud-managed instances are involved, or discontinue use if no mitigation exists.

Beyond the patch, harden the SNMP surface: migrate remaining SNMPv1/v2c instances to SNMPv3 with strong authentication and encryption, restrict source addresses with ACLs or control-plane policing, and disable SNMP entirely on interfaces or VRFs that do not require it. These steps reduce the attack surface for this and future SNMP flaws.

If you can't patch immediately

Until the fixed image can be deployed, limit exposure. Place management interfaces in a dedicated, tightly filtered VRF or out-of-band network so that only authorized NMS hosts can reach SNMP. If SNMP is not operationally required, shut the service down. Where a web application firewall or IPS sits in front of the device, enable any vendor-supplied virtual-patch signatures for this CVE once they appear; treat them as temporary. Increase monitoring of SNMP traffic and device health traps so that a sudden reload or anomalous packet pattern triggers an immediate investigation. Document the residual risk and the planned patch window for change-control and audit purposes.

If your data may have been exposed

Successful exploitation of a high-privilege remote-code-execution flaw on a network device can lead to traffic interception, credential theft, or lateral movement. While ransomware use of this specific vulnerability is not documented, any compromise of infrastructure devices should be treated as a potential breach. Review device configurations and logs for unauthorized changes, rotate any credentials or keys stored on or accessible from the affected systems, and consider a free exposure scan of administrative email addresses against known breach corpora to check for secondary credential reuse.