CVE-2026-90450: Authentication Bypass Vulnerability

CVE-2026-90450 Overview

CVE-2026-90450 is an authorization flaw where the affected application's role-authorization lookup defaults to allowing access when a request handler is not registered in its role-requirements table. Any authenticated user can reach unregistered handlers regardless of assigned role. New handlers added to the application are fail-open by default until an administrator explicitly maps them to required roles. The weakness is classified under CWE-863: Incorrect Authorization and is referenced in a CISA CSAF advisory covering industrial control system software.

Critical Impact
Authenticated users with any role can invoke request handlers that were intended to be role-restricted, enabling horizontal and vertical privilege escalation across the application's exposed functionality.

Affected Products

Specific affected product identifiers are not enumerated in the NVD record
Referenced in CISA ICSA-26-254-01 CSAF Advisory
Industrial control system software component (per CISA advisory scope)

Discovery Timeline

2026-09-11 - CVE-2026-90450 published to NVD
2026-09-18 - Last updated in NVD database

Technical Details for CVE-2026-90450

Vulnerability Analysis

The vulnerability resides in the application's role-based access control (RBAC) lookup logic. When a request arrives, the authorization component queries a table that maps request handler names to the roles permitted to invoke them. If the handler name is absent from the table, the lookup returns a permissive result rather than a deny. Authenticated users can therefore invoke any handler that was never registered, whether by oversight, incomplete configuration, or recent code changes.

The attack surface expands with every feature addition. Each newly introduced request handler is reachable by any authenticated principal until a developer or administrator explicitly registers it with the correct role requirement. This creates a persistent regression risk during normal development activity.

Root Cause

The root cause is a design default that violates the principle of secure defaults, specifically fail-closed authorization. The lookup treats a missing table entry as "no restriction" instead of "no permission granted." This inverts the expected behavior for security-critical policy decisions and aligns with the CWE-863 pattern of incorrect authorization checks.

Attack Vector

Exploitation requires network access and valid low-privilege credentials, with no user interaction. An authenticated attacker enumerates request handler endpoints exposed by the application and identifies those absent from the role-requirements table. Invoking these handlers succeeds regardless of the caller's assigned role. The impact depends on which handlers are unregistered and what functionality they expose, ranging from information disclosure to administrative actions.

Detailed exploitation code is not published. Reproduction requires environment-specific handler enumeration; consult the CISA CSAF Advisory for vendor-provided technical context.

Detection Methods for CVE-2026-90450

Indicators of Compromise

Authenticated requests to handler endpoints that do not appear in the application's documented role map
Successful HTTP 200 responses on endpoints that should return 403 Forbidden for the calling user's role
Session activity where a single low-privilege account touches administrative or sensitive handler paths

Detection Strategies

Compare application access logs against the current role-requirements table and flag any handler invocation not covered by an explicit rule
Instrument the authorization layer to emit a warning event whenever the lookup returns a default-allow decision
Perform authenticated dynamic application security testing (DAST) using a low-privilege account to enumerate handlers that respond successfully

Monitoring Recommendations

Forward application authorization decisions and access logs to a centralized analytics platform for correlation with user role context
Alert on first-seen handler invocations by any user, especially those tied to non-administrative roles
Track deployment events and reconcile newly added handlers against the role-requirements registry within the same change window

How to Mitigate CVE-2026-90450

Immediate Actions Required

Apply the vendor patch referenced in the CISA ICSA-26-254-01 advisory as soon as it is available for your deployment
Audit the current role-requirements table and add explicit entries for every request handler exposed by the application
Restrict network reachability to the application to trusted management networks until the fix is applied

Patch Information

Refer to the CISA CSAF Advisory ICSA-26-254-01 for vendor patch identifiers, fixed versions, and upgrade guidance. The NVD record does not enumerate specific fixed product versions at the time of publication.

Workarounds

Implement a wrapper or middleware that enforces a default-deny policy when the role lookup returns no match, rejecting the request with HTTP 403
Reduce the population of authenticated users where feasible and enforce least-privilege role assignment to shrink the exploitable surface
Add a startup-time validator that fails deployment if any registered handler is missing from the role-requirements table

bash

# Example reverse-proxy enforcement pattern to block unmapped handlers
# until the application-level fix is deployed.
location ~ ^/api/ {
    # Allow only explicitly permitted handler paths
    if ($request_uri !~ ^/api/(status|login|user/profile|admin/[a-z]+)$) {
        return 403;
    }
    proxy_pass http://backend;
}