Summary
CVE-2026-41005 is a critical SAML authentication bypass vulnerability in Cloud Foundry UAA (User Account and Authentication), classified CWE-347 (Improper Verification of Cryptographic Signature) with a CVSS 3.1 score of 9.0 (Critical). The flaw allows any unauthenticated attacker with network access to impersonate arbitrary users by crafting forged SAML assertions, potentially gaining full access to all UAA-protected systems. All UAA releases from v2.0.0 through v78.13.0 and all CF Deployment versions through v56.1.0 are affected.
Technical details
- Root cause: Cloud Foundry UAA incorrectly treated XML encryption (a confidentiality control) as a substitute for XML signatures (an authenticity/integrity control). When UAA received a SAML assertion that was encrypted but unsigned, it accepted the assertion as authentic — conflating the ability to decrypt ciphertext with proof that a trusted Identity Provider (IdP) issued the message.
- Why encryption is insufficient for authenticity: Encryption of SAML assertions uses the Service Provider’s (SP) public key, which is published in the SP’s metadata and freely accessible to any party on the internet. Any actor — not only a trusted IdP — can therefore produce ciphertext that UAA will decrypt. Successful decryption proves nothing about the origin of the message.
- Affected SAML flows: Two flows are vulnerable: (1) the OAuth 2.0 SAML2 bearer grant (token endpoint), and (2) browser SSO via the Assertion Consumer Service (ACS) when
wantAssertionSignedis set tofalse. - Attack vector: The SAML token endpoint and ACS are HTTP/HTTPS endpoints exposed to the network. An attacker submits a crafted SAML assertion — encrypted with the publicly available SP public key but carrying no valid IdP signature — directly to these endpoints.
- No authentication required: The attacker requires no prior credentials or session; the SP public key needed to construct the forged ciphertext is retrieved from published UAA metadata.
- Impact: Complete authentication bypass — the attacker can obtain OAuth 2.0 access tokens for any user in the system, resulting in full identity impersonation. CVSS impact metrics are Confidentiality:High, Integrity:High, Availability:High with Scope:Changed, reflecting that the compromise extends beyond UAA itself to all downstream services protected by UAA-issued tokens.
Affected software
- Cloud Foundry UAA (uaa_release): v2.0.0 through v78.13.0 (inclusive)
- Cloud Foundry CF Deployment: all versions through v56.1.0 (inclusive)
Severity
- CVSS v3.1 Base Score: 9.0 (Critical)
- Vector String:
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
Mitigation and recommended actions
- Immediate — upgrade:
- Upgrade uaa_release to v78.15.0 or later (note: v78.14.0 contains known issues and should not be used as the target version).
- Upgrade CF Deployment to v57.0.0 or later, which bundles uaa_release v78.16.0.
- If immediate patching is not feasible:
- For browser SSO flows, set
wantAssertionSigned=trueon all SAML Service Provider configurations to require IdP signatures on assertions; this removes the ACS attack surface. - Disable or restrict access to SAML2 bearer grant clients at the token endpoint where not operationally required.
- Apply network-layer controls to limit access to UAA SAML endpoints to known, trusted IdP source IP ranges.
- For browser SSO flows, set
IONIX Status
The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.