CVE-2025-20352: Cisco IOS XE SD-WAN RCE Vulnerability

CVE-2025-20352 Overview

A stack overflow vulnerability exists in the Simple Network Management Protocol (SNMP) subsystem of Cisco IOS Software and Cisco IOS XE Software. This vulnerability allows authenticated, remote attackers to cause denial of service conditions or, in specific scenarios involving Cisco IOS XE Software, execute arbitrary code as the root user.

The vulnerability presents a dual-threat scenario: low-privileged attackers with SNMPv2c or earlier read-only community strings (or valid SNMPv3 user credentials) can trigger a device reload causing a DoS condition. More critically, high-privileged attackers with administrative or privilege 15 credentials combined with SNMPv1/v2c read-only community strings or SNMPv3 credentials can achieve root-level code execution on Cisco IOS XE devices.

Critical Impact

This vulnerability is actively exploited in the wild and has been added to CISA's Known Exploited Vulnerabilities catalog. Organizations running affected Cisco IOS/IOS XE devices with SNMP enabled should prioritize remediation immediately.

Affected Products

• Cisco IOS (versions 12.2 through 15.9)
• Cisco IOS XE (versions 3.5 through 17.18)
• Cisco IOS XE SD-WAN (versions 16.9 through 16.12)

Discovery Timeline

• September 24, 2025 - CVE CVE-2025-20352 published to NVD
• October 28, 2025 - Last updated in NVD database

Technical Details for CVE-2025-20352

Vulnerability Analysis

This vulnerability stems from a stack overflow condition in the SNMP subsystem implementation within Cisco IOS and IOS XE Software. The flaw affects all versions of SNMP (v1, v2c, and v3) and can be exploited over both IPv4 and IPv6 networks.

The impact differs based on the attacker's privilege level and the target platform. On devices running Cisco IOS Software, a successful exploit causes the system to reload, resulting in service disruption. On Cisco IOS XE Software devices, the same DoS condition applies, but high-privileged attackers can additionally leverage the stack overflow to execute arbitrary code with root privileges, potentially gaining full control of the affected system.

The vulnerability is classified under CWE-121 (Stack-based Buffer Overflow), indicating that the SNMP packet processing code fails to properly validate input boundaries before writing data to a stack-allocated buffer.

Root Cause

The vulnerability is caused by improper input validation in the SNMP subsystem's packet processing functions. When the SNMP service processes specially crafted packets, it fails to adequately check the size of incoming data before copying it to stack-allocated buffers. This allows attackers to write beyond the intended buffer boundaries, corrupting adjacent stack memory including return addresses and saved registers.

The stack-based nature of this overflow makes it particularly dangerous for code execution, as attackers can overwrite the function return address to redirect execution flow to attacker-controlled code.

Attack Vector

The attack is conducted remotely over the network by sending specially crafted SNMP packets to vulnerable devices. The exploitation requirements vary based on the desired outcome:

For Denial of Service (DoS):

• Requires SNMPv2c or earlier read-only community string, OR
• Valid SNMPv3 user credentials
• Target device must have SNMP enabled and accessible

For Remote Code Execution (IOS XE only):

• Requires SNMPv1 or v2c read-only community string, OR valid SNMPv3 credentials
• Additionally requires administrative access or privilege 15 credentials on the device
• Target must be running Cisco IOS XE Software

The attack can be delivered over either IPv4 or IPv6 networks to any interface where SNMP is listening. Successful exploitation for code execution results in complete system compromise with root-level access.

Detection Methods for CVE-2025-20352

Indicators of Compromise

• Unexpected device reloads or system restarts correlated with SNMP traffic
• Unusual SNMP packets containing malformed or oversized payloads in network captures
• Crash dumps indicating stack corruption in SNMP-related processes
• Unauthorized configuration changes or unexpected root-level processes on IOS XE devices

Detection Strategies

• Monitor for abnormal SNMP traffic patterns, particularly packets with unusual sizes or malformed structures
• Implement intrusion detection signatures for SNMP stack overflow exploitation attempts
• Review system logs for SNMP-related crashes or unexpected device reloads
• Deploy network monitoring to detect SNMP traffic from unauthorized sources

Monitoring Recommendations

• Enable SNMP logging and forward logs to a centralized SIEM for correlation analysis
• Implement network flow analysis to establish SNMP traffic baselines and detect anomalies
• Configure alerts for device reload events and correlate with SNMP activity timestamps
• Monitor for privilege escalation attempts on IOS XE devices following SNMP activity

How to Mitigate CVE-2025-20352

Immediate Actions Required

• Apply Cisco security patches immediately to all affected IOS and IOS XE devices
• Restrict SNMP access using access control lists (ACLs) to trusted management networks only
• Disable SNMP on devices where it is not operationally required
• Rotate SNMP community strings and SNMPv3 credentials as a precautionary measure

Patch Information

Cisco has released security updates to address this vulnerability. Organizations should consult the Cisco Security Advisory for specific fixed software versions applicable to their deployments. Given this vulnerability's inclusion in the CISA Known Exploited Vulnerabilities Catalog, federal agencies and critical infrastructure operators should prioritize patching within CISA-mandated deadlines.

Workarounds

• Implement strict ACLs to limit SNMP access to only known and trusted management stations
• Migrate from SNMPv1/v2c to SNMPv3 with authentication and encryption for enhanced security
• Consider disabling SNMP temporarily on high-value assets until patches can be applied
• Segment network architecture to isolate management plane traffic from user and data traffic

# Example ACL configuration to restrict SNMP access
access-list 10 permit 192.168.100.0 0.0.0.255
snmp-server community <COMMUNITY_STRING> ro 10
snmp-server host 192.168.100.10 version 3 auth <USERNAME>