CVE-2026-76459 in NX-OS Software
Summary
by MITRE • 10/07/2026
As part of Cisco's ongoing commitment to proactive security and product quality, the Cisco NX-OS engineering team has conducted a comprehensive internal security review. This review resulted in a software hardening release that addresses multiple internally discovered vulnerabilities.
The vulnerabilities tracked by CVE-2026-76459 are related to out-of-bounds write issues that are grouped under the Common Weakness Enumeration (CWE) CWE-787.
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Analysis
by VulDB Data Team • 10/07/2026
Cisco NX-OS, a critical operating system powering many of the world's largest data centers and enterprise networks, has been identified as containing significant memory safety vulnerabilities in recent software releases. The Cisco engineering team conducted an extensive internal security review to proactively identify and remediate potential weaknesses before they could be exploited by adversaries. This rigorous audit process led to the discovery of several critical flaws, specifically tracked under CVE-2026-76459, which represent a class of memory corruption issues known as out-of-bounds writes. These vulnerabilities are categorized under Common Weakness Enumeration identifier CWE-787, indicating that the software is writing data beyond the boundaries of allocated buffers or arrays within its execution environment.
The technical nature of an out-of-bounds write vulnerability involves improper validation of input parameters or index values before they are used to access memory locations. In the context of Cisco NX-OS, this flaw likely occurs during the processing of specific network packets, configuration commands, or internal system states where boundary checks fail to ensure that data fits within predefined limits. When such a check is bypassed or incorrectly implemented, the application writes information into adjacent memory regions that are not intended for that purpose. This can overwrite critical control structures, function pointers, or other sensitive data stored in contiguous memory blocks. The severity of this flaw lies in its potential to corrupt the integrity of the operating system's execution flow, leading to unpredictable behavior ranging from service crashes to complete system compromise.
From an operational perspective, these vulnerabilities pose a severe risk to network infrastructure stability and security. An attacker who can trigger the vulnerable code path may achieve arbitrary code execution with the privileges of the affected process, which in many cases is root or equivalent high-level administrative access on the network device. This capability allows for full control over the switch or router, enabling the adversary to intercept traffic, modify routing tables, install persistent backdoors, or use the compromised device as a pivot point for further attacks against internal networks. The impact extends beyond immediate system availability; it undermines the trust model of the entire network segment protected by these devices. Given that NX-OS is often deployed in high-value environments handling sensitive corporate and customer data, such compromises can lead to significant financial loss, regulatory penalties, and reputational damage for affected organizations.
The classification under CWE-787 highlights a fundamental weakness in memory management practices within the software development lifecycle of the vulnerable components. This type of error is particularly dangerous because it does not require complex exploitation techniques like race conditions or logic flaws; rather, it relies on precise crafting of input data to trigger the buffer overflow condition. In terms of attack vectors and tactics, this vulnerability aligns with MITRE ATT&CK technique T1203, which covers Exploitation for Client Execution if triggered via user interaction, or more commonly in network devices, techniques related to remote code execution through protocol parsing flaws such as those found in command injection or packet processing engines. The lack of robust bounds checking represents a deviation from secure coding standards that mandate rigorous input validation and memory safety guarantees, especially in systems programming languages like C where manual memory management is prevalent.
To mitigate the risks associated with CVE-2026-76459 and similar out-of-bounds write vulnerabilities, organizations must prioritize immediate patching of Cisco NX-OS to the hardened release provided by Cisco. This involves upgrading to versions that include specific fixes for these internal security findings. Beyond software updates, network architects should implement defense-in-depth strategies such as restricting management plane access through strict Access Control Lists and limiting exposure to untrusted networks. Additionally, enabling features like control plane policing can help mitigate the impact of volumetric attacks or malformed packet floods designed to trigger these vulnerabilities. Regular vulnerability scanning and continuous monitoring for anomalous behavior on network devices are essential practices to detect potential exploitation attempts early. Furthermore, adopting secure development lifecycle principles that include static analysis tools capable of detecting buffer overflows during the coding phase can prevent such weaknesses from reaching production environments in future releases.