Cisco Fixes High-Severity IOS XR Flaws Enabling Image Bypass and DoS

Cisco has issued a security update to address multiple high-severity vulnerabilities in its IOS XR software, which can allow image verification bypass and trigger denial-of-service (DoS) conditions. The fix was published as part of the network giant's semiannual Software Security Advisory Bundled Publication on September 10, 2025.

The Vulnerabilities Fixed by Cisco

Cisco has identified several vulnerabilities in its IOS XR software that can be exploited to trigger a broadcast storm, leading to a DoS condition. The most severe of these vulnerabilities is tracked as CVE-2025-20340, which resides in the Address Resolution Protocol (ARP) implementation of Cisco IOS XR Software.

According to Cisco's security advisory, an unauthenticated adjacent attacker can exploit this vulnerability by sending an excessive amount of traffic to the management interface of an affected device, overwhelming its ARP processing capabilities. This can lead to degraded device performance, loss of management connectivity, and complete system unresponsiveness, resulting in a DoS condition.

Another high-severity issue tracked as CVE-2025-20248 (CVSS score of 6) is related to the IOS XR installation process. Attackers with root-system privileges on the affected device can bypass image signature checks, insert unsigned files into an ISO image, and install them on devices.

According to Cisco's advisory, a successful exploit of this vulnerability could allow attackers to load an unsigned file as part of the image activation process. The network giant has raised the security impact rating of this advisory from medium to high due to the potential bypass of image verification.

Cisco has also fixed a medium-severity IOS XR flaw tracked as CVE-2025-20159 (CVSS 5.3), which lets remote attackers bypass ACLs for SSH, NetConf, and gRPC due to missing ACL support in the management interface.

The networking giant notes that it is not aware of any attacks in the wild exploiting one of these vulnerabilities. However, it is essential for network administrators to apply the security patch as soon as possible to ensure the security of their devices.

What This Means for Network Administrators

The fixes addressed by Cisco are crucial for preventing potential security breaches and mitigating the risk of DoS conditions. Network administrators should apply the security patch to affected devices as soon as possible to ensure the security of their networks.

It is also essential for network administrators to stay informed about the latest security vulnerabilities and patches from reputable sources, such as Cisco's Software Security Advisory Bundled Publication. By staying proactive in addressing potential security threats, organizations can reduce their risk exposure and protect their critical infrastructure.

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