CVE-2025-20169: Cisco IOS SNMP DoS Vulnerability

CVE-2025-20169 Overview

A vulnerability in the SNMP subsystem of Cisco IOS Software and Cisco IOS XE Software could allow an authenticated, remote attacker to cause a denial of service (DoS) condition on affected devices. This vulnerability is caused by improper error handling when parsing SNMP requests, which can result in unexpected device reloads and service disruption.

Critical Impact

Successful exploitation of this vulnerability allows authenticated attackers to cause affected Cisco network devices to reload unexpectedly, resulting in denial of service conditions that can disrupt critical network infrastructure.

Affected Products

• Cisco IOS (multiple versions from 12.2 through 15.9)
• Cisco IOS XE (multiple versions from 3.2 through 17.15)
• Network devices running vulnerable SNMP configurations with versions 1, 2c, or 3

Discovery Timeline

• February 5, 2025 - CVE-2025-20169 published to NVD
• October 30, 2025 - Last updated in NVD database

Technical Details for CVE-2025-20169

Vulnerability Analysis

This vulnerability affects the SNMP subsystem in Cisco IOS and IOS XE software. The flaw resides in how the SNMP service handles and parses incoming SNMP requests. When a specially crafted SNMP request is sent to an affected device, the improper error handling in the parsing logic can trigger an unexpected device reload, effectively causing a denial of service condition.

The vulnerability affects all three versions of the SNMP protocol (versions 1, 2c, and 3). However, the exploitation requirements differ based on the SNMP version:

• For SNMP v2c or earlier: The attacker must possess a valid read-write or read-only SNMP community string
• For SNMP v3: The attacker must have valid SNMP user credentials

This authentication requirement means that exploitation is limited to attackers who have already obtained valid SNMP credentials through other means, such as credential harvesting, insider access, or weak/default community strings.

Root Cause

The root cause of this vulnerability is improper error handling when parsing SNMP requests (CWE-805). The SNMP subsystem fails to properly validate and handle certain malformed or crafted SNMP request structures, leading to a condition that causes the device to crash and reload. The vulnerability exists in the request parsing code path where insufficient boundary checks or error handling mechanisms allow malformed input to trigger fatal errors in the device software.

Attack Vector

The attack vector is network-based and requires authentication. An attacker with network access to the SNMP service (typically UDP port 161) and valid SNMP credentials can exploit this vulnerability by:

1. Establishing a connection to the target device's SNMP service
2. Sending specially crafted SNMP requests that exploit the parsing vulnerability
3. Triggering the improper error handling condition
4. Causing the device to reload unexpectedly

The attack can be executed remotely without user interaction, and successful exploitation results in device unavailability until the reload completes.

Detection Methods for CVE-2025-20169

Indicators of Compromise

• Unexpected device reloads or crashes with SNMP-related crash dump information
• High volume of SNMP requests from unusual or external IP addresses
• Repeated device reboots following SNMP traffic patterns
• System logs showing SNMP subsystem errors preceding device reloads
• Crash reports indicating memory or parsing errors in SNMP components

Detection Strategies

• Monitor SNMP traffic for anomalous request patterns or malformed packets
• Implement SNMP access logging and alert on authentication attempts from unauthorized sources
• Deploy network-based intrusion detection signatures to identify crafted SNMP exploit attempts
• Review crash logs and core dumps for SNMP-related failure signatures

Monitoring Recommendations

• Enable SNMP logging with detailed request tracking on affected devices
• Configure syslog forwarding to centralized security monitoring platforms
• Set up alerts for unexpected device reloads or rapid restart patterns
• Monitor SNMP authentication failures and unusual community string usage

How to Mitigate CVE-2025-20169

Immediate Actions Required

• Review and restrict SNMP access to only trusted management networks and hosts
• Ensure SNMP community strings are complex and not using default values
• Consider migrating to SNMP v3 with strong authentication and encryption
• Implement ACLs to limit SNMP access to authorized management stations only
• Monitor Cisco security advisories for patch availability

Patch Information

According to the Cisco Security Advisory, Cisco has disclosed this vulnerability and organizations should consult the advisory for specific software fix release information. At the time of this writing, organizations should check with Cisco for available patches for their specific IOS and IOS XE versions.

Organizations running affected versions should:

• Check the Cisco Security Advisory for fixed software releases
• Plan upgrade windows to apply patches when available
• Test patches in non-production environments before deployment

Workarounds

• Disable SNMP if not required for network management operations
• Restrict SNMP access using infrastructure ACLs to allow only authorized management hosts
• Use Control Plane Policing (CoPP) to rate-limit SNMP traffic and reduce attack surface
• Implement SNMP v3 with strong authentication and consider disabling v1 and v2c

# Configuration example - Restrict SNMP access to specific management hosts
! Apply an ACL to limit SNMP access
access-list 10 permit host 192.168.1.100
access-list 10 permit host 192.168.1.101
access-list 10 deny any log

! Apply ACL to SNMP community
snmp-server community COMPLEX_STRING ro 10

! Configure SNMPv3 with authentication and encryption
snmp-server group MGMTGROUP v3 priv
snmp-server user SNMPUSER MGMTGROUP v3 auth sha AUTH_PASSWORD priv aes 128 PRIV_PASSWORD

! Disable SNMP v1 and v2c if not required
no snmp-server community public
no snmp-server community private