Analysis Summary

Cisco has disclosed a critical zero-day vulnerability, tracked as CVE-2025-20352, affecting all supported versions of Cisco IOS and IOS XE. The flaw, already being actively exploited in the wild, impacts as many as 2 million exposed devices worldwide. It originates from a stack overflow bug in the SNMP (Simple Network Management Protocol) component, which is responsible for handling network management data. The vulnerability carries a CVSS severity score of 7.7, enabling attackers to launch denial-of-service (DoS) attacks or, in certain cases, achieve remote code execution (RCE) with root privileges. Cisco confirmed that exploitation was observed after attackers compromised local administrator credentials.

To exploit the flaw for RCE, an attacker must have access to a device’s SNMP read-only community string or valid SNMPv3 credentials. These strings are often shipped with default values, remain widely known within organizations, and sometimes are left unchanged, making them a prime target. Once exploited, attackers can escalate privileges to root, bypassing even administrative restrictions. Security researcher emphasized that achieving root-level access on Cisco devices represents a particularly severe breach, as such privileges surpass what administrators are supposed to hold.

For denial-of-service attacks, the requirements are less stringent: an attacker only needs valid SNMP credentials to crash vulnerable devices remotely. This risk is compounded by the poor security practice of exposing SNMP services directly to the Internet. Shodan scans confirm that more than 2 million Cisco devices have SNMP exposed, highlighting a massive attack surface for opportunistic and targeted campaigns alike. As a result, organizations that fail to properly restrict or monitor SNMP exposure face an elevated likelihood of compromise.