LDAP Integration Fails with TLS Certificate Verification Error Due to SHA1-Signed CA Certificate
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LDAP Integration Fails with TLS Certificate Verification Error Due to SHA1-Signed CA Certificate

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Article ID: 439906

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Updated On:

Products

VMware vDefend Firewall VMware vDefend Firewall with Advanced Threat Prevention

Issue/Introduction

LDAP integration fails while configuring or validating LDAPS connectivity in VMware vDefend Security Services Platform with the following error:

failed to dial LDAP server ldaps://<ldap-server>:636:
LDAP Result Code 200 "Network Error":
tls: failed to verify certificate:
x509: certificate signed by unknown authority
(possibly because of "x509: cannot verify signature:
insecure algorithm SHA1-RSA" while trying to verify candidate authority certificate)

Environment

SSP all versions 

Cause

The LDAPS server certificate chain contains a Certificate Authority (CA) certificate signed using the deprecated and insecure SHA1-RSA algorithm.

Modern TLS libraries and Go-based applications reject SHA-1 signed certificates because SHA-1 is considered cryptographically insecure. As a result, certificate validation fails during the TLS handshake, causing LDAP integration to fail.

This issue typically occurs when:

  • The LDAP server uses an outdated internal PKI.
  • Intermediate or root CA certificates are signed using SHA-1.

Resolution

 Recommended Resolution:

1. Review LDAP Server Certificate Chain

Run the following command from the SSPI appliance or any Linux host to inspect the full LDAPS certificate chain:

openssl s_client -connect <ldap-server>:636 -showcerts > cert.pem

This command retrieves the complete certificate chain, including:

  • Server certificate
  • Intermediate CA certificate(s)
  • Root CA certificate

2. Check Certificate Signature Algorithm

Inspect the certificate details using:

openssl x509 -in cert.pem -text -noout | grep "Signature Algorithm"

Review the output for weak hashing algorithms such as:

  • sha1WithRSAEncryption
  • sha1RSA

3. Identify Weak Certificates in the Chain

If SHA1 is detected, determine which certificate contains it:

  • Root CA certificate
  • Intermediate CA certificate
  • LDAPS (server) certificate

4. Extract Individual Certificates from the Chain

The cert.pem file will contain multiple certificates in the following format:

 -----BEGIN CERTIFICATE-----

...

-----END CERTIFICATE-----

Copy each certificate into separate files:

  • server.crt
  • intermediate.crt
  • root.crt

5. Verify Each Certificate Individually

Run the following commands for detailed inspection:

openssl x509 -in root.crt -text -noout

openssl x509 -in intermediate.crt -text -noout

openssl x509 -in server.crt -text -noout

 6. Identify SHA1-Signed Certificates

In the output, check the following field:

Signature Algorithm: sha1WithRSAEncryption

or

Signature Algorithm: sha1RSA

Any certificate using SHA1 must be replaced or reissued.

7. Reissue Certificates Using Secure Algorithms

Engage the certificate administration team to regenerate affected certificates.

Reissue using one of the following secure algorithms:

  • SHA256-RSA (minimum recommended)
  • SHA384-RSA (stronger security)
  • Other stronger algorithms supported by the Certificate Authority (CA)

8. Replace LDAPS Certificate on the LDAP Server

After reissuance, the administration team should:

  • Install the new certificate chain on the LDAP/AD server
  • Ensure the full chain is installed correctly (server + intermediate + root)

9. Revalidate LDAP Certificate Chain

Validate the updated configuration by repeating Step 1 and Step 2:

  • Confirm no SHA1-based certificates exist
  • Ensure full certificate chain is properly trusted
  • Verify LDAPS connectivity on port 636

10. Reconfigure LDAP in SSP  following the steps mentioned in following documentation: configure platform authentication providers

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WORKAROUND:

As an interim workaround for LDAP/LDAPS certificate issues, a TLS-enabled proxy will be introduced between SSPI and the LDAP server. The proxy will terminate secure connections using a valid SHA256/SHA384 certificate, and SSPI will validate only the proxy certificate instead of the backend LDAP certificate. This approach ensures secure LDAPS communication from SSPI while allowing the existing LDAP server configuration (including legacy certificates) to remain unchanged temporarily. This is a short-term mitigation until LDAP certificates are reissued with SHA256 or stronger algorithms and direct integration is restored. 

If upgrading or reissuing LDAPS certificates with SHA256-RSA or stronger is not currently feasible, a temporary workaround is to introduce a TLS-capable proxy layer between SSPI and the LDAP server by following the steps  configure-proxy-settings-ssp

 

 

 

Additional Information

if still issue persists please contact Broadcom support for further troubleshooting

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