CVE-2025-20170: Cisco IOS SNMP DoS Vulnerability

CVE-2025-20170 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 due to improper error handling when parsing SNMP requests, which can be exploited by an attacker sending crafted SNMP requests to force an unexpected device reload.

Critical Impact

An authenticated attacker can cause network infrastructure devices to reload unexpectedly, resulting in service disruption across enterprise networks relying on Cisco IOS and IOS XE powered equipment.

Affected Products

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

Discovery Timeline

• February 5, 2025 - CVE-2025-20170 published to NVD
• July 3, 2025 - Last updated in NVD database

Technical Details for CVE-2025-20170

Vulnerability Analysis

This vulnerability exists within the SNMP subsystem's request parsing functionality in Cisco IOS and IOS XE operating systems. The flaw stems from improper error handling during the parsing of SNMP requests, classified under CWE-805 (Buffer Access with Incorrect Length Value). When the SNMP subsystem receives a specially crafted request, the improper error handling triggers a condition that causes the entire device to reload unexpectedly.

The vulnerability affects all three SNMP protocol versions (1, 2c, and 3), though exploitation requirements differ based on the version in use. For SNMP v2c or earlier, an attacker must possess knowledge of a valid read-write or read-only SNMP community string. For SNMP v3, the attacker requires valid SNMP user credentials for the target system.

The exploitation is network-accessible, requires low complexity to execute, and while it requires low-level authentication, no user interaction is needed. The scope is changed, meaning the vulnerability can affect resources beyond the vulnerable component, with high availability impact but no confidentiality or integrity impact.

Root Cause

The root cause lies in improper error handling within the SNMP request parsing logic. When the SNMP subsystem encounters malformed or specifically crafted request data, the error handling routines fail to properly sanitize or reject the input, leading to a condition where buffer access occurs with an incorrect length value. This improper buffer handling ultimately triggers a system crash and unexpected reload of the device.

Attack Vector

The attack is executed remotely over the network by sending crafted SNMP requests to an affected device. The attack requires the following conditions:

1. Network Access: The attacker must have network connectivity to the target device's SNMP service
2. Authentication: Valid SNMP credentials are required:
   
   • For SNMP v1/v2c: A valid community string (read-only or read-write)
   • For SNMP v3: Valid SNMP user credentials
3. Crafted Request: The attacker sends a specially crafted SNMP request designed to trigger the parsing error
4. Exploitation Result: Upon successful exploitation, the device reloads unexpectedly, causing a Denial of Service condition

The vulnerability can be repeatedly exploited to cause sustained service disruption, as each crafted request can trigger another device reload once the system comes back online.

Detection Methods for CVE-2025-20170

Indicators of Compromise

• Unexpected device reloads with crash logs indicating SNMP-related errors
• Repeated device restarts correlating with incoming SNMP traffic patterns
• System logs showing SNMP subsystem errors or parsing failures immediately before crashes
• Anomalous SNMP request patterns from unauthorized or unexpected source IP addresses

Detection Strategies

• Monitor system logs for unexpected reload events and correlate with SNMP activity timestamps
• Implement network traffic analysis to identify malformed or unusual SNMP packets
• Deploy intrusion detection signatures specifically targeting malformed SNMP request patterns
• Configure SNMP access logging to track all SNMP authentication attempts and requests

Monitoring Recommendations

• Enable detailed SNMP logging on all Cisco IOS and IOS XE devices
• Configure syslog forwarding to centralized SIEM platforms for crash event correlation
• Implement SNMP traffic baseline monitoring to detect anomalous request volumes or patterns
• Set up automated alerts for unexpected device reloads across network infrastructure

How to Mitigate CVE-2025-20170

Immediate Actions Required

• Review and restrict SNMP access using access control lists (ACLs) to limit connections to trusted management stations only
• Rotate SNMP community strings and credentials if potential compromise is suspected
• Consider temporarily disabling SNMP on non-critical devices until patches can be applied
• Implement network segmentation to isolate management plane traffic from general network access
• Monitor affected devices closely for unexpected reload events

Patch Information

Cisco has released security updates to address this vulnerability. Organizations should consult the Cisco Security Advisory for specific patched software versions and upgrade guidance. Apply patches according to your organization's change management procedures, prioritizing internet-facing and critical infrastructure devices.

Workarounds

• Implement SNMP access restrictions using infrastructure ACLs to permit SNMP connections only from known, trusted management IP addresses
• If not required for operations, disable SNMP entirely on affected devices until patching is complete
• For SNMP v3 deployments, ensure strong authentication credentials and consider implementing additional access controls
• Use SNMPv3 with authentication and encryption instead of SNMPv1 or SNMPv2c where possible to reduce the attack surface

# Example: Configure SNMP access restriction on Cisco IOS
# Restrict SNMP access to specific management networks only

access-list 10 permit 10.0.0.0 0.0.0.255
access-list 10 deny any log

snmp-server community <YOUR_COMMUNITY_STRING> RO 10
snmp-server host 10.0.0.100 <YOUR_COMMUNITY_STRING>

# For SNMPv3, configure authentication and encryption
snmp-server group MGMT-GROUP v3 priv
snmp-server user MGMT-USER MGMT-GROUP v3 auth sha <AUTH_PASS> priv aes 256 <PRIV_PASS>