IBM Sterling File Gateway SSO Authentication Bypass

Technical Analysis

The vulnerability stems from improper validation of an SSO (Single Sign-On) header used by IBM Sterling File Gateway during session establishment, allowing an unauthenticated remote attacker to inject or spoof header values and gain a fully privileged authenticated session. This class of flaw is typically exploited by intercepting or crafting HTTP requests that include the trusted SSO header field, bypassing identity provider validation entirely. Once authenticated, an attacker could access, exfiltrate, or manipulate files and configuration data managed by the gateway, potentially pivoting to connected backend systems. Organizations that expose Sterling File Gateway to partner networks or the internet for B2B file exchange are at highest risk of exploitation. Where AI agents or automated pipelines use Sterling File Gateway as a data ingestion or RAG source for document/file transfers, this bypass could allow attackers to inject poisoned files or exfiltrate credentials and API keys stored in transferred configuration files, indirectly compromising downstream agent workflows.

Affected Systems

IBM Sterling File Gateway (all deployments using SSO header-based authentication); specific affected versions per IBM Security Bulletin (pending vendor confirmation); applies to on-premises and hybrid cloud deployments where SSO integration is enabled

Indicators of Compromise

• No public IOCs available at time of disclosure; monitor for anomalous authenticated sessions originating without corresponding SSO/IdP login events
• Unusual HTTP requests containing manipulated or duplicate SSO header values (e.g., X-SSO-User, X-Forwarded-User)
• Unexpected administrative or file-access activity from IPs not associated with known partner/B2B endpoints

Remediation Steps

1. 1

   Apply Vendor Patch

   Monitor IBM Security Bulletins and apply the official fix for CVE-2026-75878 as soon as it is released.

2. 2

   Restrict SSO Header Trust

   Configure reverse proxies/load balancers to strip and re-set SSO headers from external clients, ensuring only the identity provider can set these values.

3. 3

   Network Segmentation

   Limit exposure of Sterling File Gateway management and SSO endpoints to trusted internal networks or VPN-only access.

4. 4

   Session and Access Auditing

   Review authentication logs for sessions established without corresponding SSO provider login events, and rotate credentials/API keys accessible via the gateway.

5. 5

   Web Application Firewall Rules

   Deploy WAF rules to detect and block requests with anomalous or duplicated SSO header fields until patching is complete.