Description

An issue in MongoDB Server's intra-cluster connection setup could allow a party with suitable network access to influence which authentication mechanism is used when one replica set member connects to another. Under certain conditions, this could cause the cluster's shared internal credential to be transmitted in a less-protected form, potentially allowing that credential to be recovered. If recovered, the credential could be used to authenticate as the internal superuser to nodes in the deployment.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "8.8",
  "pubDate": "2026-08-11T19:17:22.903Z",
  "pubdate": "2026-08-11T19:17:22.903Z",
  "executiveSummary": "An authentication downgrade vulnerability exists in the intra-cluster connection setup mechanism of MongoDB Server. The security flaw allows an unauthorized entity with suitable network access to manipulate the negotiation process, dictating the specific authentication mechanism employed during inter-node communication between replica set members.\nUnder specific operational conditions, successful exploitation forces the transmission of the cluster's shared internal credential using a less-protected format. This degradation in cryptographic protection exposes the credential to interception and subsequent offline recovery.\nThe primary impact of this vulnerability involves the complete compromise of internal cluster authentication. If an attacker successfully recovers the shared internal credential, they can leverage it to authenticate as the internal superuser across any node within the entire MongoDB deployment.\nThe risk implications are severe, as unauthorized superuser access grants full administrative control over the database instances, potentially leading to data exfiltration, modification, or destruction.\nExploitation requirements include suitable network access to the intra-cluster communication channels and the ability to intercept or influence the protocol handshake where authentication mechanisms are negotiated between replica set members. The affected product is MongoDB Server.",
  "technicalDetails": "The vulnerability resides within the intra-cluster connection setup and negotiation logic of MongoDB Server. The root cause stems from insufficient validation and enforcement of robust authentication mechanisms during the handshake phase when one replica set member initiates a connection to another.\nThe vulnerable component is the internal node-to-node communication protocol handler responsible for establishing authenticated sessions using shared internal credentials. Because the system permits undue external influence over the mechanism selection process, an adversary positioned on the network path can manipulate the negotiation parameters.\nThe attack flow proceeds as follows: First, the attacker establishes suitable network access to intercept or observe traffic traversing the intra-cluster network boundaries. Second, as a replica set member initiates a connection setup sequence to another member, the attacker interferes with the authentication mechanism negotiation phase. Third, by forcing the communicating nodes to fall back to a less-protected authentication mechanism, the protocol circumvents stronger cryptographic protections normally applied to internal traffic.\nConsequently, the cluster's shared internal credential is transmitted in this weakened or less-protected form over the network. The payload behavior involves capturing this vulnerable transmission. Once intercepted, the attacker subjects the captured credential data to recovery techniques, such as offline cryptanalysis or brute-force extraction, depending on the exact nature of the degraded mechanism.\nUpon successful recovery of the internal credential, the post-exploitation impact is critical. The attacker utilizes the recovered credential to authenticate directly to nodes in the deployment, assuming the privileges of the internal superuser. This grants unrestricted administrative access to the underlying database systems, bypassing standard security controls and enabling full administrative control over the cluster."
}