On September 24, 2025, Cisco Systems issued security advisory CVE-2025-20352, which communicated a security vulnerability related to its Cisco IOS Software and Cisco IOS XE Software. Cisco IOS and Cisco IOS XE are operating systems that run on a variety of Cisco devices, such as Cisco routers, switches, and wireless controllers. IOS XE is the more modern of the two.
According to Cisco, this vulnerability specifically concerns the Simple Network Management Protocol (SNMP). SNMP is a widely used protocol for managing and monitoring network devices. This is a high-severity zero-day vulnerability that is already being exploited in the wild. Cisco says that all versions of SNMP are affected. The Cisco Security Advisory is a key source for this article.
Technical Explanation of Vulnerability CVE-2025-20352
Cisco outlines a couple of different exploitation scenarios in the Security Advisory, saying “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”. It states that this vulnerability affects any devices running Cisco IOS and IOS XE that have SNMP enabled. As for the attack vector, it would involve crafted SNMP packets over IPv4/IPv6.
Mayuresh Dani, Security Research Manager at Qualys Threat Research Unit, explained that “CVE-2025-20352 is a stack-based buffer overflow vulnerability in the Simple Network Management Protocol (SNMP) subsystem of Cisco IOS and IOS XE software. Threat actors can exploit this flaw by transmitting specially crafted SNMP packets to vulnerable devices over both IPv4 and IPv6 networks.” He added that the risk is amplified because “SNMP is commonly enabled for network management purposes, making a large percentage of Cisco’s installed base potentially vulnerable until patches are applied and configurations are hardened.”
Mitigation and Workaround for Cisco Security Vulnerability CVE-2025-20352
Cisco recommends in its Security Advisory that customers deploy software patches to remediate the situation. It indicates that there is no workaround that would mitigate the impact of the vulnerability. Cisco also describes in detail mitigation steps in the Security Advisory. One example is that teams can restrict SNMP to trusted hosts/users as a temporary mitigation measure. Refer to the Security Advisory for full details on the mitigation measures.
Security Takeaways
There are few of takeaways here. The first is that there are serious risks to leaving critical network infrastructure unpatched. Teams should prioritize implementing patches for critical vulnerabilities as soon as possible to minimize the risk. Second, there is a broader lesson on monitoring with SNMP and the use of privileged credentials.
Qualys’ Dani stressed that the SNMP subsystem has been abused before, including by groups such as APT28, emphasizing that the pattern of exploitation around Cisco IOS XE continues to evolve rather than disappear.
Patching alone, however, isn’t enough. Jason Soroko, Senior Fellow at Sectigo, advises treating this as “an immediate risk to network availability and the integrity of core infrastructure.” He recommends that security teams “triage exposure now, build an inventory of IOS and IOS XE systems with SNMP enabled, patch to fixed releases starting with internet-facing and core nodes, and disable SNMP where it is not required.” Until full remediation is possible, Soroko said, organizations should “restrict SNMP to trusted management subnets with tight access controls and monitor for unusual SNMP traffic or device restarts.”
Beyond this single incident, there’s a broader principle at work: validating inputs and minimizing trust. Krishna Vishnubhotla, Vice President of Product Strategy at Zimperium, drew a parallel to the mobile landscape, explaining that “one malicious input is often all it takes. Cisco’s router flaw demonstrates how weak validation allows attackers to slip in crafted payloads. The same is true for mobile apps—attackers can reverse these apps, map the APIs, and feed them a malicious payload.” In both cases, the problem isn’t just a software defect; it’s misplaced trust in data and privileges.
The “principle of least privilege” is a tried-and-true concept in IT in which administrators are given only the level of access needed to perform their job functions. Reducing the number of privileged accounts also reduces the risk.
