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CVE-2025-20352: Cisco IOS XE SNMP Heap Overflow RCE Analysis

By Ammar Khan, CEH · October 18, 2026 · CybernytronX Research
CVE-2025-20352: Cisco IOS XE SNMP Heap Overflow RCE Analysis

In October 2025, Cisco disclosed a critical heap overflow vulnerability in the SNMP subsystem of Cisco IOS XE Software, tracked as CVE-2025-20352. According to Cisco's security advisory, the flaw allows an authenticated, remote attacker to execute arbitrary code with root privileges on affected devices. While proof-of-concept code has been published, Cisco's Product Security Incident Response Team (PSIRT) has not observed active exploitation in the wild as of the advisory date. This article provides a deep technical analysis of the vulnerability, its root cause, potential attacker tactics, detection opportunities, and mitigation strategies. By the end, you will understand the mechanics of the heap overflow, how to identify vulnerable devices, and how to harden your network against this class of threat.

Background: The SNMP Heap Overflow

CVE-2025-20352 is a heap-based buffer overflow vulnerability in the Simple Network Management Protocol (SNMP) subsystem of Cisco IOS XE Software. The vulnerability exists because the software insufficiently validates the length of user-supplied input before copying it to a heap buffer. An attacker could exploit this by sending a crafted SNMP request to an affected device. A successful exploit could allow the attacker to cause a denial of service (DoS) condition or execute arbitrary code with root privileges. Cisco has assigned a CVSS score of 8.8 (High) with the vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H, reflecting the need for authentication (PR:L) but high impact on confidentiality, integrity, and availability. The vulnerability was discovered internally by Cisco and disclosed in a security advisory on October 15, 2025. At the time of disclosure, Cisco PSIRT was not aware of any malicious use of the vulnerability.

SNMP is widely used for network management and monitoring, and is often enabled on Cisco devices with default or weak community strings. Although the vulnerability requires authentication, attackers may obtain credentials through SNMP community string guessing, credential stuffing, or prior compromise. The heap overflow occurs in the processing of SNMP requests, potentially allowing an attacker to overwrite heap memory and hijack control flow. Cisco's advisory notes that the vulnerability is in the SNMP server code, and exploitation could lead to remote code execution.

Affected Versions

Cisco has published a detailed list of affected and fixed software versions in its advisory. The vulnerability affects Cisco IOS XE Software releases prior to the first fixed release. The following table summarizes the affected and fixed releases:

Administrators should consult the Cisco advisory for the most up-to-date information and for any additional affected products. Cisco has also provided a software checker tool to help identify vulnerable devices.

Attacker TTPs

While no active exploitation has been reported, the vulnerability could be exploited by attackers using techniques consistent with MITRE ATT&CK. The following techniques are relevant:

It is important to note that these are potential TTPs based on the nature of the vulnerability; no specific ransomware gang has been observed exploiting CVE-2025-20352 as of this writing.

Detection

Detecting exploitation attempts requires monitoring SNMP traffic and device logs. The following Sigma rule detects suspicious SNMP requests that may indicate exploitation attempts. It looks for SNMP SET requests with unusually large payloads or specific OIDs known to be targeted.

title: Suspicious SNMP Request with Large Payload
id: 5f8a3c2e-1b4d-4e7f-9a6c-8d2e1f3b4c5d
status: experimental
description: Detects SNMP requests with large payloads that may indicate exploitation of CVE-2025-20352
author: CybernytronX
logsource:
  product: snmp
  service: snmp
detection:
  selection:
    pdu_type: 'SetRequest'
    payload_size: '> 1000'
  condition: selection
falsepositives:
  - Legitimate large SNMP SET requests
level: high

Additionally, network monitoring can use Suricata rules to detect anomalous SNMP traffic. The following rule alerts on SNMP SET requests with a specific OID that may be targeted:

alert udp any any -> any 161 (msg:"Possible CVE-2025-20352 SNMP Heap Overflow Attempt"; content:"|a2|"; offset:0; depth:1; content:"|01 03 06 01 02 01 04 01 09|"; distance:0; within:10; classtype:attempted-admin; sid:1000001; rev:1;)

Note: The above rules are illustrative and may require tuning for your environment. Cisco has not released specific detection signatures.

Mitigation

Cisco recommends upgrading to a fixed software release as listed in the advisory. If immediate upgrade is not possible, administrators should consider the following mitigations:

For detailed instructions, refer to the Cisco advisory. Cisco has also provided a security advisory with workarounds, including disabling SNMP or applying ACLs.

Why This Matters for Defenders

Network devices are high-value targets for attackers because they provide a foothold into the core of the network. A compromised router or switch can be used to pivot to other systems, intercept traffic, or disrupt operations. While CVE-2025-20352 requires authentication, many organizations use weak SNMP community strings or reuse credentials, making exploitation feasible. Defenders should prioritize patching network infrastructure and enforce strong SNMP configurations. Given the potential for ransomware actors to leverage such vulnerabilities for initial access, it is critical to include network devices in vulnerability management and incident response plans.

Sources

Frequently Asked Questions

Is CVE-2025-20352 being exploited in the wild?

As of the Cisco advisory date (October 15, 2025), Cisco PSIRT was not aware of any malicious use of the vulnerability. However, proof-of-concept code has been published, and administrators should monitor for updates.

What is the CVSS score of CVE-2025-20352?

Cisco has assigned a CVSS base score of 8.8 (High) with vector CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.

Which Cisco products are affected?

The vulnerability affects Cisco IOS XE Software. A full list of affected and fixed releases is available in the Cisco advisory. Other Cisco products may also be affected; refer to the advisory for details.

How can I detect if my device is vulnerable?

You can use the Cisco Software Checker tool or manually verify the software version against the fixed releases listed in the advisory.

What should I do if I cannot patch immediately?

Disable SNMP if not needed, or restrict SNMP access to trusted hosts using ACLs. Use SNMPv3 with strong authentication and encryption.

Does this vulnerability affect SNMPv3?

The vulnerability is in the SNMP server code and may affect all SNMP versions. However, exploitation requires authentication, so using SNMPv3 with strong credentials reduces risk.

Need expert help with this?

CybernytronX specializes in network security assessments, vulnerability management, and incident response. Our team can help you identify exposed SNMP services, prioritize patches, and implement robust monitoring. Explore our Ethereon AI threat detection platform for continuous anomaly detection across your infrastructure. Contact us at cybernytronx.com/contact.html to discuss how we can support your security posture.

AK

Ammar Khan — Founder, CybernytronX

Certified Ethical Hacker (CEH), B.S. Cybersecurity, Google Certified. 5+ years pentesting, creator of Ethereon AI threat detection. Has remediated 50+ environments and recovered 20+ compromised domains. Hire CybernytronX →

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