CVE-2026-18691: CWE-757: Selection of Less-Secure Algorithm During Negotiation ('Algorithm Downgrade') in MongoDB MongoDB Server
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.
AI Analysis
Technical Summary
This vulnerability (CWE-757) in MongoDB Server's intra-cluster connection negotiation allows an attacker with suitable network access to influence the authentication mechanism used between replica set members. Under certain conditions, this can cause the cluster's shared internal credential to be transmitted using a less-secure algorithm, potentially enabling the attacker to recover the credential. If the credential is recovered, it can be used to authenticate as the internal superuser to nodes within the deployment, compromising cluster security.
Potential Impact
An attacker with network access to the MongoDB cluster can cause the internal superuser credential to be transmitted in a less-protected form, potentially allowing credential recovery. This would enable the attacker to authenticate as the internal superuser on any node in the cluster, leading to full control over the deployment.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. No official fix or temporary workaround has been documented at this time. Until a fix is available, restrict network access to intra-cluster communication channels to trusted parties only.
CVE-2026-18691: CWE-757: Selection of Less-Secure Algorithm During Negotiation ('Algorithm Downgrade') in MongoDB MongoDB Server
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.
CVSS v4.0
Score 9.0critical
Affected software
MongoDB
MongoDB Server
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
This vulnerability (CWE-757) in MongoDB Server's intra-cluster connection negotiation allows an attacker with suitable network access to influence the authentication mechanism used between replica set members. Under certain conditions, this can cause the cluster's shared internal credential to be transmitted using a less-secure algorithm, potentially enabling the attacker to recover the credential. If the credential is recovered, it can be used to authenticate as the internal superuser to nodes within the deployment, compromising cluster security.
Potential Impact
An attacker with network access to the MongoDB cluster can cause the internal superuser credential to be transmitted in a less-protected form, potentially allowing credential recovery. This would enable the attacker to authenticate as the internal superuser on any node in the cluster, leading to full control over the deployment.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. No official fix or temporary workaround has been documented at this time. Until a fix is available, restrict network access to intra-cluster communication channels to trusted parties only.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- mongodb
- Date Reserved
- 2026-08-03T15:53:04.081Z
- Cvss Version
- 4.0
- State
- PUBLISHED
Threat ID: 6a7b7422bf8831d539467f72
Added to database: 08/11/2026, 19:12:34 UTC
Last enriched: 08/11/2026, 19:28:43 UTC
Last updated: 09/25/2026, 01:47:41 UTC
Views: 64
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