CVE-2026-76504

A vulnerability in the API session-based authentication management of Cisco Catalyst SD-WAN Manager could allow an unauthenticated, remote attacker to access…

Critical Known exploited

Severity: 9.8 / 10; Critical · CVSS 3.1
Exploit chance (EPSS): 38.93%; Chance of exploitation in the next 30 days. Higher than 98.59% of scored vulnerabilities.
Known exploited: Yes; In CISA's catalog since Sep 30, 2026
Weakness: CWE-177 Improper Handling of URL Encoding (Hex Encoding)
Fix: None yet; No fixed version published

Exploited in the wild. Cisco Catalyst SD-WAN Manager Hex Encoding Vulnerability (Cisco Catalyst SD-WAN Manager). Required action: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines. Due for U.S. federal agencies by Oct 3, 2026.

Description

A vulnerability in the API session-based authentication management of Cisco Catalyst SD-WAN Manager could allow an unauthenticated, remote attacker to access an affected system with privileges of the admin user.

This vulnerability is due to improper handling of URI encoding in an HTTP request, which allows the request to bypass an authentication rule that is intended to restrict access to a specific API endpoint. An attacker could exploit this vulnerability by sending a crafted HTTP request to the API of the affected system. A successful exploit could allow the attacker to bypass authentication and gain access to the API as the admin user.

How to fix

No fixed version has been published yet. Until one is, remove or replace the package, or turn off or isolate the affected feature. This page updates when a fix ships.

Severity breakdown

CVSS 3.1 9.8

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: High
Availability: High

Weakness

CWE-177: Improper Handling of URL Encoding (Hex Encoding)

The product does not properly handle when all or part of an input has been URL encoded.

How to prevent it

Architecture and Design: Avoid making decisions based on names of resources (e.g. files) if those resources can have alternate names.
Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
Implementation: Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.

References

Advisories

sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-sdwan-webauth…

Timeline

Sep 30, 2026 Added to CISA's Known Exploited Vulnerabilities catalog
Sep 30, 2026 Published
Oct 3, 2026 Remediation due for U.S. federal agencies
Oct 3, 2026 Last updated by the source
Oct 31, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GHSA-jqff-g426-hqxp fast-uri vulnerable to host confusion via percent-encoded scheme normalization	High	Same weakness, CWE-177
GHSA-x428-ghpx-8j92 @fastify/static vulnerable to route guard bypass via encoded path separators	Medium	Same weakness, CWE-177
GHSA-q5qw-h33p-qvwr Hono vulnerable to arbitrary file access via serveStatic vulnerability	Critical	Same weakness, CWE-177
GHSA-fvhj-4qfh-q2hm Traefik incorrectly processes fragment in the URL, leads to Authorization Bypass	Medium	Same weakness, CWE-177
GHSA-g8q8-fggx-9r3q Keycloak vulnerable to path traversal via double URL encoding	Critical	Same weakness, CWE-177

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