CVE-2026-75878: IBM Sterling File Gateway Auth Bypass Flaw

CVE-2026-75878 Overview

CVE-2026-75878 is an authentication bypass vulnerability in IBM Sterling File Gateway. A remote attacker can obtain a fully authenticated session by supplying an unvalidated single sign-on (SSO) header. The flaw is classified under Improper Authentication [CWE-287] and is exploitable over the network without prior credentials or user interaction.

Successful exploitation grants the attacker an authenticated session in the file transfer platform. This exposes managed file transfer workflows, partner data, and administrative functions to unauthorized access and modification.

Critical Impact
An unauthenticated remote attacker can forge an SSO header to obtain a fully authenticated Sterling File Gateway session, exposing sensitive B2B file transfer data and administrative operations.

Affected Products

IBM Sterling File Gateway (refer to the IBM Support Documentation for affected versions)

Discovery Timeline

2026-09-18 - CVE-2026-75878 published to NVD
2026-09-22 - Last updated in NVD database

Technical Details for CVE-2026-75878

Vulnerability Analysis

CVE-2026-75878 stems from improper handling of a single sign-on header used to establish authenticated user context in IBM Sterling File Gateway. The application trusts the SSO header value without validating its origin or cryptographic integrity. An attacker can supply an arbitrary header value in an HTTP request and receive a session tied to any user identity, including privileged accounts.

Sterling File Gateway is an enterprise managed file transfer (MFT) platform used to exchange files with business partners. A session obtained through this bypass allows the attacker to view partner routing configurations, download or replace files in transit, and modify gateway workflows.

Root Cause

The root cause is missing validation of the SSO header on inbound requests, categorized as [CWE-287] Improper Authentication. When SSO integration is enabled, the gateway accepts the header as an authoritative assertion of identity. It does not verify that the header originated from a trusted reverse proxy or identity provider, nor does it require a signed token to accompany the assertion.

Attack Vector

Exploitation requires only network access to the Sterling File Gateway web interface. The attacker sends an HTTP request containing the crafted SSO header naming a target user account. The gateway returns a valid session cookie bound to that identity. No credentials, tokens, or user interaction are required.

No public proof-of-concept code has been released. Refer to the IBM Support Documentation for technical details.

Detection Methods for CVE-2026-75878

Indicators of Compromise

Inbound HTTP requests to Sterling File Gateway containing SSO headers originating from source IP addresses outside the trusted reverse proxy or identity provider range.
Authenticated sessions established without corresponding authentication events in the identity provider logs.
Unexpected administrative actions, partner configuration changes, or file downloads attributed to accounts that did not interactively log in.

Detection Strategies

Correlate Sterling File Gateway access logs with upstream identity provider logs to identify sessions that lack a matching SSO authentication event.
Inspect HTTP request headers at the perimeter to identify direct requests carrying SSO headers that bypass the sanctioned reverse proxy.
Alert on session creation events where the user-agent, IP geolocation, or access pattern deviates from established baselines for privileged users.

Monitoring Recommendations

Enable verbose authentication logging in Sterling File Gateway and forward logs to a centralized SIEM for correlation.
Monitor for anomalous file transfer volumes, new partner definitions, or workflow modifications that follow suspicious session creation.
Track administrative API calls and configuration changes with change-control review to catch unauthorized activity quickly.

How to Mitigate CVE-2026-75878

Immediate Actions Required

Apply the IBM security update referenced in the IBM Support Documentation as the primary remediation.
Restrict network access to the Sterling File Gateway management and web interfaces to trusted networks and reverse proxies only.
Invalidate active sessions and rotate service account credentials after patching to remove any sessions established through the bypass.

Patch Information

IBM has published remediation guidance for CVE-2026-75878. Administrators should consult the IBM Support Documentation for the affected version list and the fixed release identifiers, then schedule an expedited upgrade.

Workarounds

Configure the upstream reverse proxy or web application firewall to strip inbound SSO headers from all client requests, allowing the header only when injected by the trusted proxy after authentication.
Enforce mutual TLS or IP allowlisting between the identity provider or reverse proxy and Sterling File Gateway so that only trusted intermediaries can assert SSO identity.
Disable SSO integration temporarily and require direct authentication if patching cannot be completed promptly.

bash

# Example: strip client-supplied SSO headers at an NGINX reverse proxy
# Adjust header name to match the SSO header used by your deployment
location / {
    proxy_set_header SM_USER "";
    proxy_set_header iv-user "";
    proxy_pass https://sterling-file-gateway.internal;
}