Cisco IOS and IOS XE SNMP Subsystem Stack Overflow Vulnerability (CVE-2025-20352) Technical Advisory
Executive & SecOps Summary
SECOPS ASSESSMENTAll versions of Cisco IOS and Cisco IOS XE Software with active SNMP services
Authenticated attackers can trigger a system reload (DoS) or execute arbitrary code with root privileges (RCE) via crafted SNMP packets
Apply official Cisco software updates immediately, restrict SNMP access via ACLs, or disable unused SNMP services
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Upgrade to the latest Cisco recommended release for your platform. Below is an example of upgrading the IOS XE image via TFTP.
# Verify current software version and storage space
show version
show file systems
# Download the patched IOS XE image from your secure TFTP server
copy tftp: flash:
# Address or name of remote host? 192.168.1.100
# Source filename? cat3k_caa-universalk9.16.12.08.SPA.bin
# Destination filename [cat3k_caa-universalk9.16.12.08.SPA.bin]?
# Configure the boot system path and save configuration
configure terminal
no boot system
boot system flash:cat3k_caa-universalk9.16.12.08.SPA.bin
end
write memory
reload2. Temporary Workaround & Hardening Configuration
If patching cannot be performed immediately, restrict SNMP access to trusted management hosts using Access Control Lists (ACLs).
configure terminal
# Define an ACL allowing only trusted management hosts (e.g., 10.1.1.50)
ip access-list standard SNMP_ALLOW_ACL
permit 10.1.1.50
deny any log
exit
# Apply the ACL to existing SNMP communities
snmp-server community public RO SNMP_ALLOW_ACL
snmp-server community private RW SNMP_ALLOW_ACL
# Disable SNMP entirely if it is not required
no snmp-server
end
write memory3. Log Audit & IoC Verification Commands
Inspect the device configuration and system logs to identify unauthorized SNMP configurations or unexpected reloads.
# Check active SNMP configurations and community strings
show running-config | include snmp-server
# Audit system logs for unexpected reloads or SNMP anomalies
show version | include returned to ROM
show logging | include %SNMP|%SYS-5-RELOADStop Exposing VPN Ports to the Internet — Switch to Zero-Trust Access
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Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2025-20352) is a stack-based buffer overflow (CWE-121) within the Simple Network Management Protocol (SNMP) subsystem of Cisco IOS and Cisco IOS XE Software. The root cause lies in insufficient input validation when processing incoming SNMP packets, allowing an attacker to overflow the stack memory space over IPv4 or IPv6 networks.
2. Exploitation Mechanics & Attack Scenario
To exploit this vulnerability, the attacker must possess valid SNMP credentials (such as SNMPv1/v2c read-only community strings or valid SNMPv3 user credentials).
- Denial of Service (DoS): A low-privileged authenticated attacker can send a crafted SNMP packet to trigger a stack overflow, causing the device to crash and reload.
- Remote Code Execution (RCE): On Cisco IOS XE, a high-privileged attacker (possessing privilege 15 credentials in addition to SNMP credentials) can leverage the stack overflow to execute arbitrary code as the root user, gaining full administrative control.
3. Infrastructure & Business Impact
As this vulnerability is listed in the CISA KEV catalog, active exploitation has been observed in the wild. A successful exploit on core routing and switching infrastructure can lead to widespread network outages (DoS) or allow threat actors to establish a persistent foothold within the enterprise network.
Official Vendor Advisories & References
A vulnerability in the Simple Network Management Protocol (SNMP) subsystem of Cisco IOS Software and Cisco IOS XE Software could allow the following: An authenticated, remote attacker with low privileges could cause a denial of service (DoS) condition on an affected device that is running Cisco IOS Software or Cisco IOS XE Software. To cause the DoS, the attacker must have the SNMPv2c or earlier read-only community string or valid SNMPv3 user credentials. An authenticated, remote attacker with high privileges could execute code as the root user on an affected device that is running Cisco IOS XE Software. To execute code as the root user, the attacker must have the SNMPv1 or v2c read-only community string or valid SNMPv3 user credentials and administrative or privilege 15 credentials on the affected device. An attacker could exploit this vulnerability by sending a crafted SNMP packet to an affected device over IPv4 or IPv6 networks. This vulnerability is due to a stack overflow condition in the SNMP subsystem of the affected software. A successful exploit could allow a low-privileged attacker to cause the affected system to reload, resulting in a DoS condition, or allow a high-privileged attacker to execute arbitrary code as the root user and obtain full control of the affected system. Note: This vulnerability affects all versions of SNMP.
Frequently Asked SecOps Questions (CVE-2025-20352)
FAQQ1. How critical is CVE-2025-20352 and is it actively exploited in the wild?
CVE-2025-20352 is rated CVSS 7.7 (HIGH) with a 30-day EPSS exploitation probability of 40.6%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2025-20352?
Primary impacted vendors include cisco across ios, ios_xe. Scope summary: All Cisco IOS and Cisco IOS XE Software versions configured with active SNMPv1, v2c, or v3 services
Q3. What temporary mitigations or workarounds exist for CVE-2025-20352 before patching?
[Mitigation] Apply official Cisco software updates immediately, restrict SNMP access via ACLs, or disable unused SNMP services Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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