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Cisco Issues Urgent Warning on Exploited IOS Zero-Day Vulnerability

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The disclosure of a high-severity zero-day vulnerability in Cisco IOS and IOS XE Software exposes a critical weakness in the Simple Network Management Protocol (SNMP) subsystem. Tracked as CVE-2025-20352, the flaw is already being actively exploited in the wild, placing countless organizations at immediate risk. Systems with SNMP enabled are particularly vulnerable, as the flaw could allow attackers to launch denial-of-service (DoS) attacks or potentially execute malicious code remotely. Cisco has released urgent security updates, urging administrators to apply patches and limit SNMP access to trusted networks to mitigate the threat.

Vulnerability Details

SNMP Remote Code Execution Vulnerability (CVE-2025-20352)

CVE-2025-20352 is a high-severity vulnerability in the SNMP subsystem of Cisco IOS and IOS XE Software, allowing authenticated attackers to trigger a stack-based buffer overflow. By sending specially crafted SNMP requests, attackers can cause device reloads (DoS) or potentially achieve remote code execution on affected systems.

The flaw stems from improper bounds checking when parsing SNMP Object Identifiers (OIDs), leading to memory corruption. Devices with SNMP enabled, regardless of version (v1, v2c, or v3), are vulnerable.

Exploiting this bug could give attackers control over network infrastructure, making it a serious threat, especially as it is being actively exploited in the wild. Cisco has released patches, and administrators are urged to update devices, limit SNMP access, and monitor for suspicious activity.

Exploitation

CVE-2025-20352 (Cisco software local privilege escalation vulnerability):

Attackers exploit a local privilege escalation vulnerability in Cisco software after compromising local Administrator credentials.
By leveraging this flaw, attackers can elevate privileges and gain broader system access. Active exploitation in the wild underscores the urgency of patching affected systems.

Affected Products

Cisco IOS and IOS XE SNMP subsystem

Tactics, Techniques, and Procedures (TTPs)

  • TA0001 – Initial Access: Exploiting public-facing applications or remote services to gain initial access.
  • TA0002 – Execution: Executing malicious code on a compromised system.
  • TA0040 – Impact: Causing a denial-of-service condition.
  • T1190 – Exploit Public-Facing Application: Exploiting software vulnerabilities in an internet-facing computer system, network, or device.
  • T1210 – Exploitation of Remote Services: Use of software bugs or security holes to cause unintended or unanticipated behavior on a remote system, network, or device.
  • T1499 – Endpoint Denial of Service: Preventing the availability of services.

Impact

  • Low Privilege Attackers: Authenticated remote attackers with limited privileges (for example, valid SNMP community strings or low privilege SNMPv3 credentials) can trigger denial of service (DoS) conditions (device crash/reload) on unpatched Cisco IOS/IOS XE devices.
  • High Privilege Attackers: Attackers with elevated privileges can exploit the flaw to achieve remote code execution and full system compromise (execute code as root) on vulnerable devices.

Mitigation & Recommendations

  • Apply security patches provided by Cisco to all affected IOS and IOS XE systems.
  • Restrict SNMP access to trusted IP ranges or management networks using ACLs or firewall rules.
  • Disable SNMP on devices where it is not required to reduce the attack surface.
  • Monitor network traffic for unusual SNMP activity or repeated device reloads as indicators of potential exploitation.

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