CVE-2025-20174 Overview
Cisco disclosed CVE-2025-20174, a high-severity denial of service (DoS) vulnerability in the Simple Network Management Protocol (SNMP) subsystem of Cisco IOS Software and Cisco IOS XE Software. An authenticated, remote attacker can send a crafted SNMP request to trigger improper error handling, causing the affected device to reload unexpectedly. The flaw affects SNMP versions 1, 2c, and 3, requiring either a valid community string (v1/v2c) or valid user credentials (v3). The vulnerability is tracked under [CWE-805] (Buffer Access with Incorrect Length Value) and impacts a broad range of Cisco IOS 15.x and IOS XE 3.x through 17.x releases.
Critical Impact
Successful exploitation causes affected routers and switches to reload, disrupting network availability across the infrastructure managed by the device.
Affected Products
- Cisco IOS Software (multiple 15.x trains)
- Cisco IOS XE Software (3.x, 16.x, and 17.x release trains)
- Devices with SNMP v1, v2c, or v3 enabled
Discovery Timeline
- 2025-02-05 - CVE-2025-20174 published to NVD
- 2025-07-03 - Last updated in NVD database
Technical Details for CVE-2025-20174
Vulnerability Analysis
The vulnerability resides in the SNMP request parser within Cisco IOS and IOS XE Software. Improper error handling during the processing of crafted SNMP protocol data units (PDUs) leads to an unrecoverable condition that forces the device to reload. The flaw maps to [CWE-805], indicating that the SNMP subsystem performs buffer access using an incorrect length value when handling malformed input.
Because SNMP operates over UDP and is widely deployed for network management, exposure is broad across enterprise routing and switching fabrics. The change scope is altered, meaning a single compromised SNMP daemon can disrupt routing or switching for downstream systems that depend on the device. With an EPSS probability of 0.804% (74th percentile), the vulnerability has measurably elevated exploitation likelihood compared to baseline CVEs.
Root Cause
The SNMP subsystem fails to correctly validate or bound input during PDU parsing. When the parser encounters a malformed or unexpected field, the resulting error path does not gracefully recover, leading to a process crash that triggers a full device reload. No memory corruption or code execution is described, only an availability impact.
Attack Vector
Exploitation requires network reachability to the SNMP listener (typically UDP/161) and valid authentication material. For SNMP v1 or v2c, the attacker needs a valid read-only or read-write community string. For SNMP v3, the attacker needs valid user credentials. Once authenticated, sending a single crafted SNMP request is sufficient to reload the device.
No public exploit code is available, and CVE-2025-20174 is not listed in the CISA Known Exploited Vulnerabilities catalog. Refer to the Cisco Security Advisory for the authoritative technical write-up.
Detection Methods for CVE-2025-20174
Indicators of Compromise
- Unexpected device reloads correlated with inbound SNMP traffic in syslog or show version uptime records
- Crash dumps referencing the SNMP engine process on affected IOS or IOS XE devices
- Bursts of SNMP requests from a single source preceding a device reboot
Detection Strategies
- Monitor SNMP request volume and source diversity against management baselines, alerting on requests from non-management subnets
- Correlate device reload events with SNMP traffic flows using NetFlow or IPFIX telemetry
- Audit SNMP community strings and v3 credentials for unauthorized use, especially read-write strings
Monitoring Recommendations
- Forward Cisco syslog and crashinfo files to a centralized SIEM for correlation with network telemetry
- Track SNMP authentication failures and successful authentications from unusual sources
- Establish alerting on %SYS-5-RELOAD and %SNMP log messages on managed devices
How to Mitigate CVE-2025-20174
Immediate Actions Required
- Apply Cisco's fixed software releases as documented in the Cisco Security Advisory cisco-sa-snmp-dos-sdxnSUcW
- Restrict SNMP access using infrastructure ACLs that permit only authorized management hosts
- Rotate SNMP community strings and v3 credentials if compromise is suspected
Patch Information
Cisco has released fixed software for Cisco IOS and IOS XE. Consult the vendor advisory for the specific first-fixed releases that correspond to your deployed train, including the affected 15.x, 16.x, and 17.x branches. No workaround eliminates the vulnerability without patching.
Workarounds
- Apply SNMP view restrictions to limit accessible Object Identifiers (OIDs) for read-write users
- Enforce ACLs on the snmp-server community and snmp-server group configurations to limit source IPs
- Disable SNMP entirely on devices where it is not required for management
# Configuration example: restrict SNMP to a trusted management host
access-list 99 permit host 198.51.100.10
access-list 99 deny any log
!
snmp-server community <STRING> RO 99
snmp-server group ADMINS v3 priv access 99
!
! Verify and audit existing SNMP configuration
show running-config | include snmp-server
show snmp user
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
