Summary
CVE-2026-76504 is a critical authentication bypass vulnerability in Cisco Catalyst SD-WAN Manager. Improper handling of URI encoding allows remote attackers without credentials to circumvent an authentication rule protecting an API endpoint and gain access with administrator privileges. Cisco has confirmed exploitation in the wild, and the vulnerability was added to CISA’s Known Exploited Vulnerabilities (KEV) catalog on September 30, 2026. Affected versions require upgrading to the corresponding fixed releases to address the vulnerability.
Urgent Actions Required
- Upgrade affected systems: Install the applicable Cisco-fixed release: 20.9.10.1, 20.12.8.2, 20.15.6.1, 20.18.4.1, 26.1.2.1, or 26.2.1. For releases earlier than 20.9, migrate to a supported release.
- Restrict management access: Limit access to the SD-WAN Manager interface to trusted management hosts and use network access controls to reduce exposure.
- Investigate potential exploitation: Review serviceproxy-access.log for requests containing /%6a_security_check and vmanage-server.log for suspicious viptela-reserved- user accounts.
Which Systems Are Vulnerable to CVE-2026-76504?
Technical Overview
- Vulnerability Type: Authentication Bypass Through Improper URI Encoding (CWE-177)
- Affected Software/Versions:
- Cisco Catalyst SD-WAN Manager versions earlier than 20.9.10.1
- Versions 20.12.x earlier than 20.12.8.2
- Versions 20.15.x earlier than 20.15.6.1
- Versions 20.18.x earlier than 20.18.4.1
- Versions 26.1.x earlier than 26.1.2.1
- Version 26.2 earlier than 26.2.1
- CVSS Vector: v3.1
- Attack Vector: Network
- Attack Complexity: Low
- Privileges Required: None
- User Interaction: None
- Scope: Unchanged
- Confidentiality Impact: High
- Integrity Impact: High
- Availability Impact: High
- Patch Availability: Yes, available
How Does the CVE-2026-76504 Exploit Work?
The attack typically follows these steps:
What Causes CVE-2026-76504?
Vulnerability Root Cause:
CVE-2026-76504 results from improper URI encoding handling in Cisco Catalyst SD-WAN Manager’s API authentication process. The authentication filter fails to normalize certain encoded characters before checking access permissions, allowing crafted requests to bypass authentication rules and reach protected API endpoints without credentials.
How Can You Mitigate CVE-2026-76504?
If immediate patching is delayed or not possible:
- Restrict SD-WAN Manager access to trusted management IP addresses.
- Place the management interface behind an authenticated VPN or bastion host.
- Block direct external access to the management interface.
- Monitor serviceproxy-access.log for /%6a_security_check requests.
- Review vmanage-server.log for suspicious viptela-reserved- user accounts.
Which Assets and Systems Are at Risk?
- Asset Types Affected:
- SD-WAN Management Platforms - Cisco Catalyst SD-WAN Manager (formerly vManage) running vulnerable versions.
- Management APIs - Protected API endpoints susceptible to authentication bypass through improper URI encoding.
- Enterprise WAN Infrastructure - Managed network environments where compromised administrative access could affect connected WAN Edge devices and network configurations.
- Business-Critical Systems at Risk:
- Network Management Systems - Unauthorized administrative access could expose configurations and enable changes to network settings.
- WAN Edge Devices - Attackers with management-plane access could alter configurations on downstream devices.
- Enterprise Network Connectivity - Malicious changes to routing or network settings could disrupt communications across the WAN.
- Exposure Level:
- Internet-Accessible Management Interfaces - Systems reachable by remote attackers are at risk because exploitation requires no authentication.
- Internally Accessible Management Interfaces - Restricting access reduces exposure, but unpatched systems remain vulnerable to attackers who can reach the interface.
How Can You Detect CVE-2026-76504 Exploitation?
Exploitation Signatures:
- Check serviceproxy-access.log for requests containing /%6a_security_check.
- Review vmanage-server.log for suspicious accounts with names beginning viptela-reserved-.
- Investigate unusual API requests containing encoded URI sequences that may indicate authentication bypass attempts.
Indicators of Compromise (IOCs/IOAs):
- Requests containing /%6a_security_check in access logs.
- Unexpected viptela-reserved- accounts recorded in server logs.
- Suspicious API activity consistent with unauthorized administrative access.
Alerting Strategy:
- Priority: Critical
- Alert on requests containing /%6a_security_check.
- Flag unexpected viptela-reserved- accounts for investigation.
- Investigate suspicious API activity that could indicate unauthorized access to SD-WAN Manager.
Remediation & Response
- Remediation Timeline:
- Immediate: Restrict access to Cisco Catalyst SD-WAN Manager to trusted management hosts and prevent direct access from untrusted networks.
- As soon as possible: Upgrade affected installations to the appropriate Cisco-fixed release: 20.9.10.1, 20.12.8.2, 20.15.6.1, 20.18.4.1, 26.1.2.1, or 26.2.1. Deployments running versions earlier than 20.9 should migrate to a supported release.
- After remediation: Confirm that the deployed version includes the relevant fix and review the specified logs for signs of attempted exploitation or suspicious account activity.
- Incident Response Considerations:
- Examine serviceproxy-access.log for requests containing /%6a_security_check, which Cisco identifies as a potential exploitation indicator.
- Review vmanage-server.log for unexpected accounts with names beginning viptela-reserved-.
- Investigate suspicious API activity to determine whether unauthorized administrative access may have occurred.
- Prioritize remediation because Cisco has reported active exploitation of this vulnerability, which can allow unauthenticated remote attackers to obtain administrator-level access.
Compliance & Governance Notes
- Audit Trail Requirement:
- Review and retain relevant entries from serviceproxy-access.log, focusing on requests containing /%6a_security_check.
- Examine vmanage-server.log for unexpected accounts beginning with viptela-reserved-.
- Document the affected SD-WAN Manager versions and the fixed releases deployed during remediation.
- Record investigation findings related to suspicious API activity and potential unauthorized administrative access.
- Policy Alignment:
- Strengthen access restrictions for Cisco Catalyst SD-WAN Manager so that its management interface is reachable only from trusted hosts.
- Require review of the specified logs for indicators associated with CVE-2026-76504.
- Prioritize upgrades to Cisco's fixed releases as part of vulnerability remediation, since the vendor has not provided an official workaround.
- Include this vulnerability in security reviews of exposed SD-WAN management interfaces, considering Cisco's confirmation of active exploitation.
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CVSS Breakdown Table
| Metric | Value | Description |
|---|---|---|
| Base Score | 9.8 | A critical vulnerability that can be exploited remotely without authentication and has high potential impact on confidentiality, integrity, and availability |
| Attack Vector | Network | An attacker can target the vulnerable SD-WAN Manager over a network |
| Attack Complexity | Low | Exploitation is rated as low complexity in the CVSS v3.1 vector |
| Privileges Required | None | The attacker does not need authenticated access before exploiting the vulnerability |
| User Interaction | None | Exploitation does not require action from another user |
| Scope | Unchanged | The CVSS v3.1 assessment marks the scope as unchanged |
| Confidentiality Impact | High | Successful exploitation can provide administrator-level access, potentially exposing sensitive configuration information |
| Integrity Impact | High | Unauthorized administrative access could allow changes to SD-WAN settings |
| Availability Impact | High | The CVSS vector rates availability impact as high; unauthorized administrative access could threaten network operations |
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