CVE-2026-90447: Authentication Bypass Vulnerability

CVE-2026-90447 Overview

CVE-2026-90447 is an authentication bypass vulnerability caused by improper trust in a client-supplied request header [CWE-290]. A routing rule selects between two authentication mechanisms for the same downstream service based on a header value the client can manipulate. An authenticated user in possession of a shared service credential can set this header to bypass the primary role-based authorization check. The alternate path applies a fixed, elevated role, granting access to actions reserved for higher-privileged users. CISA published the issue in Industrial Control Systems advisory ICSA-26-254-01.

Critical Impact
A low-privileged authenticated attacker with knowledge of a shared credential can perform privileged actions on the downstream service by manipulating a single request header.

Affected Products

Affected product details are published in CISA Security Advisory ICSA-26-254-01
Vendor and product identifiers are Not Available in the current NVD record
Deployments relying on header-based routing to authentication backends should be reviewed

Discovery Timeline

2026-09-11 - CVE-2026-90447 published to NVD
2026-09-18 - Last updated in NVD database

Technical Details for CVE-2026-90447

Vulnerability Analysis

The flaw resides in the request-routing layer that fronts a downstream service. The routing rule inspects a client-supplied header to decide which of two authentication mechanisms to invoke. Because the selector is client-controlled rather than derived from a trusted property, a caller can steer their request onto the alternate authentication path. The alternate path validates a shared service credential and then assigns a fixed, elevated role to the caller. This bypasses the primary role-based access control that would normally apply to that user.

The result is a horizontal-to-vertical privilege escalation confined to service integrity: attackers gain the ability to modify or invoke privileged operations without gaining confidentiality or availability impact on the surrounding system. Because the affected system is documented in a CISA ICS advisory, operational technology deployments are likely in scope.

Root Cause

The root cause is authentication logic that makes a trust decision using an attacker-controllable input, matching the pattern described by [CWE-290: Authentication Bypass by Spoofing]. The routing tier treats a request header as an authoritative signal about which authentication policy applies. No server-side property, such as the network origin, mTLS identity, or a signed token claim, constrains which authentication mechanism the request may reach. Combined with a shared service credential on the alternate path, the design collapses two distinct authorization tiers into one attacker-selectable choice.

Attack Vector

Exploitation requires network access to the routing endpoint, valid authentication as any low-privileged user, and possession of the shared service credential used by the alternate authentication path. The attacker crafts an otherwise normal request and sets the routing header to the value that selects the alternate mechanism. The routing layer forwards the request through the second authentication path, which authenticates the shared credential and applies the elevated fixed role. The downstream service then processes the request under that elevated role. No user interaction is required, and attack complexity is low.

No public proof-of-concept or in-the-wild exploitation has been reported. See CISA Security Advisory ICSA-26-254-01 for the authoritative technical description.

Detection Methods for CVE-2026-90447

Indicators of Compromise

Requests from low-privileged user sessions that also carry the routing header used to select the alternate authentication mechanism
Successful authentications on the alternate path where the source identity does not match the expected service-to-service caller
Downstream audit log entries showing privileged actions attributed to the fixed elevated role but originating from user-facing network segments

Detection Strategies

Correlate reverse-proxy or API gateway logs with downstream service logs to flag sessions whose primary user role does not match the role recorded after authentication
Alert on any request that combines an interactive user session cookie or token with the routing header that selects the service-to-service path
Baseline the legitimate callers of the shared service credential and treat any deviation in source IP, user agent, or mTLS identity as suspicious

Monitoring Recommendations

Enable verbose logging of all request headers used in routing decisions at the gateway tier
Forward gateway and downstream authentication events to a centralized analytics platform for cross-tier correlation
Review authentication events for the shared service credential daily until a patched version is deployed

How to Mitigate CVE-2026-90447

Immediate Actions Required

Consult CISA Security Advisory ICSA-26-254-01 and apply the vendor-supplied fix as soon as it is available
Rotate the shared service credential used by the alternate authentication path and restrict its distribution
Restrict network reachability of the routing endpoint to trusted management segments where feasible

Patch Information

Patch availability is tracked in the referenced CISA advisory. Vendor and product identifiers are not populated in the current NVD entry, so operators should verify affected versions and remediation guidance directly through the advisory and their vendor's support channel.

Workarounds

Strip or override the routing header at the perimeter for all requests originating from untrusted or user-facing networks
Enforce that the alternate authentication path is reachable only via mTLS or an equivalent server-verified identity, not via a client-supplied header
Split the shared service credential into per-caller credentials and remove the fixed elevated role from any path that authenticates user-tier callers