CVE-2026-47840: UAA LDAP Authentication Bypass Vulnerability

CVE-2026-47840 Overview

CVE-2026-47840 is a certificate validation flaw in Cloud Foundry User Account and Authentication (UAA) that unconditionally disables hostname verification during LDAP StartTLS connections. An attacker positioned between UAA and the LDAP directory can present any certificate signed by any trusted certificate authority (CA) and successfully impersonate the directory. The impersonated endpoint captures the LDAP bind password, harvests every end-user password sent through simple-bind authentication, and returns forged group memberships that grant administrative scopes. The flaw affects every deployment that authenticates users against LDAP over StartTLS.

Critical Impact
Adversaries can steal LDAP bind and end-user credentials in plaintext, then forge group memberships to escalate to administrative scopes across UAA-protected platforms.

Affected Products

Cloud Foundry UAA versions prior to v78.13.0
Cloud Foundry cf-deployment versions prior to v56.2.0
Any Cloud Foundry deployment configured to authenticate users against LDAP over StartTLS

Discovery Timeline

2026-07-09 - CVE-2026-47840 published to NVD
2026-07-09 - Last updated in NVD database

Technical Details for CVE-2026-47840

Vulnerability Analysis

UAA establishes LDAP connections over StartTLS to protect bind credentials in transit. The client upgrades a plaintext LDAP session to TLS after the initial handshake. Correct TLS behavior requires the client to validate that the server certificate presented during the upgrade matches the expected LDAP hostname. UAA disables this hostname verification unconditionally when StartTLS is used. The client accepts any certificate chain that terminates in a trusted CA, regardless of the subject or subject alternative name.

This reduces authentication of the directory to "any certificate from any trusted CA." A network attacker who can intercept traffic between UAA and the directory can present a valid certificate issued for an unrelated domain and complete the TLS handshake. UAA then transmits the LDAP bind credentials and every user simple-bind password to the attacker in plaintext-over-TLS. The attacker relays or fabricates LDAP search responses, including group memberships, which UAA maps to internal scopes such as administrative roles.

Root Cause

The root cause is missing hostname verification during the StartTLS upgrade in the LDAP client used by UAA. The TLS layer validates the certificate chain against the trust store but omits the SAN and CN match against the target directory hostname. This is a certificate validation bypass ([CWE-297]-class weakness) rather than a protocol flaw.

Attack Vector

Exploitation requires an active network position between UAA and the LDAP directory. Suitable positions include compromised routers, ARP or DNS spoofing on the internal network, malicious BGP announcements, or a hostile hop in a shared cloud fabric. The attacker terminates the StartTLS handshake using any leaf certificate issued by any CA present in the UAA truststore. Once the tunnel is established, the attacker records the bind DN and password, records every user simple-bind password, and returns crafted memberOf or group search results that place the attacker into administrator groups mapped to UAA scopes such as scim.write or uaa.admin. Technical details are documented in the Cloud Foundry advisory for CVE-2026-47840.

Detection Methods for CVE-2026-47840

Indicators of Compromise

Unexpected TLS certificates presented on LDAP connections from UAA, particularly certificates whose subject or SAN does not match the configured directory hostname.
UAA audit events showing new logins that resolve to administrative scopes for accounts that historically lacked those group memberships.
LDAP directory logs showing no matching bind or search activity that correlates with successful UAA authentications during the same window.

Detection Strategies

Compare the certificate fingerprint observed on UAA-to-LDAP traffic against a known-good fingerprint captured from the directory server and alert on any deviation.
Correlate UAA user_authentication_success events with directory-side bind events; investigate authentications that appear in UAA logs but not in LDAP server logs.
Monitor for sudden scope elevations, especially uaa.admin, scim.write, or custom admin scopes, granted through LDAP group mapping.

Monitoring Recommendations

Enable and centralize UAA audit logging along with LDAP directory access logs to support cross-source correlation.
Deploy network monitoring on the UAA-to-LDAP path to detect ARP spoofing, unexpected routing changes, and TLS certificate substitution.
Track outbound connections from UAA instances to identify LDAP sessions terminating at unexpected IP addresses or ASNs.

How to Mitigate CVE-2026-47840

Immediate Actions Required

Upgrade UAA to v78.13.0 or later and cf-deployment to v56.2.0 or later on all foundations that use LDAP authentication.
Rotate the LDAP bind account password after patching, since it may have been transmitted to an interceptor.
Force password resets for end users who authenticated through LDAP simple-bind while the vulnerable version was deployed.
Audit UAA group-to-scope mappings for unexpected members holding administrative scopes and revoke unauthorized grants.

Patch Information

The fix restores hostname verification during the LDAP StartTLS upgrade. It is shipped in UAA v78.13.0 and rolled into cf-deploymentv56.2.0. Full remediation notes are published in the Cloud Foundry advisory for CVE-2026-47840.

Workarounds

Switch LDAP configuration from StartTLS on port 389 to LDAPS on port 636, which is not affected by the StartTLS-specific bypass in vulnerable versions.
Restrict the CA list in the UAA truststore to only the internal CA that issues the directory certificate, reducing the set of certificates an attacker can present.
Isolate UAA-to-LDAP traffic on a dedicated network segment with strict layer-2 controls to reduce the feasibility of an on-path position until patching is complete.

bash

# Configuration example: pin UAA LDAP to LDAPS as an interim measure
# In cf-deployment ops-file / UAA config
ldap:
  url: "ldaps://ldap.internal.example.com:636"
  ssl:
    skipVerification: false
  base:
    userDn: "cn=uaa-bind,ou=service,dc=example,dc=com"