CVE-2026-22734: Cloud Foundry UAA Auth Bypass Vulnerability

CVE-2026-22734 Overview

Cloud Foundry User Account and Authentication (UAA) contains an authentication bypass vulnerability that allows an attacker to obtain tokens for any user and gain unauthorized access to UAA-protected systems. This vulnerability exists when SAML 2.0 bearer assertions are enabled for a client, as the UAA improperly accepts SAML 2.0 bearer assertions that are neither signed nor encrypted.

Critical Impact

Attackers can bypass authentication entirely by crafting unsigned SAML 2.0 bearer assertions, allowing them to impersonate any user and gain access to all UAA-protected resources within affected Cloud Foundry deployments.

Affected Products

• Cloud Foundry UAA versions v77.30.0 through v78.7.0 (inclusive)
• Cloud Foundry Deployment versions v48.7.0 through v54.14.0 (inclusive)
• Cloud Foundry environments with SAML 2.0 bearer assertions enabled for clients

Discovery Timeline

• April 17, 2026 - CVE-2026-22734 published to NVD
• April 17, 2026 - Last updated in NVD database

Technical Details for CVE-2026-22734

Vulnerability Analysis

This authentication bypass vulnerability (CWE-290: Authentication Bypass by Spoofing) stems from improper validation of SAML 2.0 bearer assertions in Cloud Foundry's UAA component. The core issue is that UAA fails to enforce signature verification and encryption requirements on incoming SAML assertions when processing bearer token requests.

In a properly configured SAML 2.0 implementation, bearer assertions must be cryptographically signed by the identity provider (IdP) to ensure authenticity, and may also be encrypted to protect confidentiality. The vulnerable UAA versions accept assertions that lack these critical security controls, allowing an attacker to craft arbitrary assertions without possessing the IdP's signing credentials.

The vulnerability specifically impacts environments where SAML 2.0 bearer assertions are configured as an authentication mechanism. When exploited, an attacker can forge assertions claiming to be any user in the system, effectively bypassing all authentication controls. This grants unauthorized access to any UAA-protected application or service within the Cloud Foundry deployment.

Root Cause

The root cause lies in missing validation logic within the UAA SAML assertion processing code. When a SAML 2.0 bearer assertion is submitted for token exchange, the UAA fails to verify that the assertion contains a valid cryptographic signature from a trusted IdP. Additionally, there is no enforcement of encryption requirements that would prevent assertion tampering in transit. This allows unsigned, unencrypted assertions to be accepted as valid authentication credentials.

Attack Vector

The attack vector is network-based and requires no authentication or user interaction. An attacker with network access to the UAA token endpoint can exploit this vulnerability by:

1. Identifying a Cloud Foundry deployment using vulnerable UAA versions with SAML 2.0 bearer assertions enabled
2. Crafting a SAML 2.0 bearer assertion with an arbitrary user identity
3. Submitting the unsigned assertion to the UAA token endpoint
4. Receiving a valid access token for the spoofed user identity
5. Using the obtained token to access UAA-protected resources as the impersonated user

The vulnerability mechanism allows attackers to forge SAML assertions without requiring access to the identity provider's signing credentials. An attacker constructs a SAML assertion containing the target user's identity and submits it to the UAA token endpoint. Because the vulnerable UAA versions do not validate the cryptographic signature or encryption status of the assertion, the forged assertion is accepted as legitimate, and a valid OAuth token is issued. For detailed technical information, see the Cloud Foundry Security Advisory.

Detection Methods for CVE-2026-22734

Indicators of Compromise

• SAML assertions submitted to UAA token endpoints that lack XML digital signatures
• Unusual token generation patterns for multiple distinct user accounts from a single source IP
• Authentication events where the SAML assertion issuer does not match expected identity provider configurations
• High volume of token requests with SAML grant type from unexpected network sources

Detection Strategies

• Monitor UAA audit logs for token grants using SAML 2.0 bearer assertion grant type and correlate with IdP authentication records
• Implement network-level inspection to detect SAML assertions without ds:Signature elements being submitted to UAA endpoints
• Deploy alerts for authentication patterns where users receive tokens without corresponding IdP login events
• Review UAA configuration to identify clients with SAML bearer assertions enabled and assess exposure

Monitoring Recommendations

• Enable detailed audit logging on UAA components to capture all token grant requests with full assertion metadata
• Implement SIEM rules to correlate UAA token issuance with identity provider authentication logs
• Monitor for lateral movement patterns following any UAA token grants that cannot be correlated to legitimate IdP authentications
• Track changes to UAA client configurations, particularly enabling of SAML bearer assertion grants

How to Mitigate CVE-2026-22734

Immediate Actions Required

• Upgrade Cloud Foundry UAA to version v78.8.0 or later immediately
• Upgrade Cloud Foundry Deployment to version v54.15.0 or later
• Disable SAML 2.0 bearer assertion grants for all UAA clients until patching is complete
• Review audit logs for any indicators of exploitation during the exposure window

Patch Information

Cloud Foundry has released security updates to address this vulnerability. Organizations should upgrade to UAA version v78.8.0 or later and CF Deployment version v54.15.0 or later. The fix implements proper validation of SAML assertion signatures and enforces encryption requirements as per the SAML 2.0 specification. For detailed patch information and upgrade guidance, refer to the Cloud Foundry Security Advisory.

Workarounds

• Disable SAML 2.0 bearer assertion grants for all clients by removing the urn:ietf:params:oauth:grant-type:saml2-bearer grant type from client configurations
• Implement network-level controls to restrict access to UAA token endpoints to trusted network segments only
• Deploy a Web Application Firewall (WAF) rule to reject SAML assertions that do not contain valid signature elements
• Consider temporarily disabling SAML-based authentication entirely and switching to alternative authentication mechanisms until patching is complete

# Configuration example - Disable SAML bearer grants for a UAA client
# Review and update client configurations in your UAA deployment manifest
# Remove 'urn:ietf:params:oauth:grant-type:saml2-bearer' from authorized_grant_types

uaac target https://uaa.example.com
uaac token client get admin -s <admin-secret>
uaac client update <client-id> --authorized_grant_types "authorization_code,refresh_token"