Cisco Patches Critical Zero-Day Authentication Bypass in Catalyst SD-WAN Manager

Cisco Systems has released security updates to address a critical zero-day vulnerability in Cisco Catalyst SD-WAN Manager that allows attackers to bypass authentication and gain remote administrator access. The flaw, tracked as CVE-2026-76504, stems from improper URI encoding handling in HTTP requests targeting specific APIs. With a CVSS v3.1 base score of 9.8, the issue is rated Critical and has already been exploited in real-world attacks confirmed by Cisco in September 2026. The company published its security advisory on September 30, 2026, and strongly recommends immediate updates to the fixed releases. Organizations are also advised to restrict API access to trusted sources while applying the patches.

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Cisco Systems has issued security updates for Cisco Catalyst SD-WAN Manager after discovering a zero-day vulnerability that is already being actively exploited in the wild.

The company disclosed the issue in a security advisory published on September 30, 2026. The vulnerability, identified as CVE-2026-76504, is an authentication bypass flaw caused by improper handling of URI encoding in HTTP requests.

By sending specially crafted requests to certain APIs, an attacker can circumvent access controls and obtain remote administrative privileges without valid credentials. The flaw received a CVSS v3.1 base score of 9.8 and is rated Critical, the highest severity level.

Cisco confirmed that it observed exploitation of the vulnerability during September 2026. To address the issue, the company released the following fixed versions: 26.2.1, 26.1.2.1, 20.18.4.1, 20.15.6.1, 20.12.8.2, and 20.9.10.1.

Customers are urged to apply the updates as soon as possible. In addition to patching, Cisco recommends restricting access to the management interfaces and APIs to trusted sources only.

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