CVE-2025-3085: MongoDB Server Auth Bypass Vulnerability

CVE-2025-3085 Overview

A critical certificate validation bypass vulnerability exists in MongoDB Server running on Linux systems when TLS and CRL (Certificate Revocation List) revocation status checking is enabled. Under these specific conditions, the server fails to properly check the revocation status of intermediate certificates in the peer's certificate chain, potentially allowing connections using revoked certificates to be established.

This improper certificate validation (CWE-299) can lead to authentication bypass scenarios, particularly when MONGODB-X509 authentication is enabled. While MONGODB-X509 is not enabled by default, organizations using this authentication method are at significant risk. The vulnerability also impacts intra-cluster authentication, potentially compromising the security of MongoDB replica sets and sharded clusters.

Critical Impact

Attackers with access to revoked intermediate certificates could potentially authenticate to MongoDB servers or intercept intra-cluster communications, bypassing TLS security controls designed to prevent use of compromised certificates.

Affected Products

• MongoDB Server v5.0 versions prior to 5.0.31
• MongoDB Server v6.0 versions prior to 6.0.20
• MongoDB Server v7.0 versions prior to 7.0.16
• MongoDB Server v8.0 versions prior to 8.0.4

Discovery Timeline

• April 1, 2025 - CVE-2025-3085 published to NVD
• September 24, 2025 - Last updated in NVD database

Technical Details for CVE-2025-3085

Vulnerability Analysis

This vulnerability represents a significant flaw in MongoDB's TLS certificate chain validation logic on Linux systems. When CRL revocation checking is enabled, the server correctly validates the end-entity certificate's revocation status but fails to extend this validation to intermediate certificates in the chain.

The impact is particularly severe for deployments utilizing MONGODB-X509 client certificate authentication, where proper certificate chain validation is essential for security. An attacker possessing a client certificate signed by a revoked intermediate CA could potentially authenticate successfully, as the server would not detect that the intermediate certificate has been revoked.

The vulnerability requires a specific configuration to be exploitable: the MongoDB Server must be running on Linux, and CRL revocation status checking must be explicitly enabled. This configuration, while not the default, is commonly deployed in security-conscious environments that require comprehensive certificate validation.

Root Cause

The root cause lies in incomplete implementation of the certificate revocation checking logic within MongoDB's TLS subsystem on Linux platforms. While the server performs revocation status verification for leaf certificates, the code path responsible for validating intermediate certificates in the chain does not properly invoke CRL checking, creating a gap in the certificate validation process.

Attack Vector

This vulnerability is exploitable over the network without requiring authentication or user interaction. An attacker would need to obtain a valid client certificate that was signed by a now-revoked intermediate CA. Even though the intermediate CA's certificate has been added to the CRL, MongoDB would still accept connections using certificates signed by that intermediate.

The attack scenario involves:

1. An intermediate CA certificate is compromised and subsequently revoked by the root CA
2. The attacker possesses or obtains client certificates signed by this revoked intermediate
3. Despite the intermediate being on the CRL, MongoDB accepts the client certificate as valid
4. The attacker gains authenticated access to the MongoDB server or can establish trusted intra-cluster connections

The vulnerability mechanism involves the TLS handshake process where certificate chain validation occurs. When a client presents its certificate chain during authentication, MongoDB's validation logic on Linux systems checks the CRL for the client's leaf certificate but skips this check for intermediate certificates in the chain. This allows certificates signed by revoked intermediates to pass validation. For detailed technical information, refer to the MongoDB JIRA Issue SERVER-95445.

Detection Methods for CVE-2025-3085

Indicators of Compromise

• Successful TLS connections from clients using certificates signed by intermediate CAs that appear on the configured CRL
• Authentication successes for MONGODB-X509 users where the certificate chain includes revoked intermediates
• Unexpected intra-cluster connections that should have been rejected based on certificate revocation policies
• Log entries showing successful certificate validation for certificate chains that include known-revoked intermediate certificates

Detection Strategies

• Audit MongoDB server logs for TLS connection events and cross-reference certificate chains against current CRLs
• Implement external certificate chain validation before traffic reaches MongoDB to detect revoked intermediate certificates
• Deploy network monitoring to identify connections using certificate chains that include certificates on published CRLs
• Review authentication logs for MONGODB-X509 authentication successes and validate the complete certificate chain manually

Monitoring Recommendations

• Enable verbose TLS logging in MongoDB to capture complete certificate chain information for each connection
• Implement monitoring for the specific MongoDB versions affected by this vulnerability across your infrastructure
• Set up alerts for authentication patterns that may indicate exploitation of certificate validation bypasses
• Monitor CRL update processes to ensure revocation lists are current and properly distributed

How to Mitigate CVE-2025-3085

Immediate Actions Required

• Upgrade MongoDB Server to patched versions: 5.0.31, 6.0.20, 7.0.16, or 8.0.4 depending on your deployment
• Audit current TLS configurations to identify systems using CRL revocation checking on Linux platforms
• Review certificate chains in use to identify any that may include previously revoked intermediate certificates
• Consider temporarily implementing additional certificate validation at the application or network layer until patches are applied

Patch Information

MongoDB has released security patches addressing this vulnerability. Affected deployments should upgrade to the following minimum versions:

For complete details on the fix, refer to the MongoDB JIRA Issue SERVER-95445.

Workarounds

• If immediate patching is not possible, consider implementing OCSP (Online Certificate Status Protocol) as an alternative revocation checking mechanism
• Deploy a reverse proxy or TLS termination point that performs complete certificate chain validation including intermediate certificate revocation checking
• Temporarily disable MONGODB-X509 authentication and use alternative authentication mechanisms until patching is complete
• Implement network segmentation to limit exposure of vulnerable MongoDB instances while patches are being deployed

# Verify current MongoDB version
mongod --version

# Check TLS and CRL configuration in mongod.conf
grep -A 10 "net:" /etc/mongod.conf | grep -E "tls|ssl|CRL"

# After upgrading, verify the new version
mongod --version