CVE-2026-18691

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 v3 8.8 HIGH

8.8^/10

CVSS v3 : HIGH

Vector :

Exploitability : 2.8 / Impact : 5.9

Attack Vector ADJACENT_NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact HIGH

Integrity Impact HIGH

Availability Impact HIGH

Scope UNCHANGED

References

Link	Resource
https://jira.mongodb.org/browse/SERVER-130264

Configurations

No configuration.

History

No history.

Information

Published : 2026-08-11 19:17

Updated : 2026-08-28 21:16

NVD link : CVE-2026-18691

Mitre link : CVE-2026-18691

CVE.ORG link : CVE-2026-18691

JSON object : View

Products Affected

No product.

CWE

CWE-757

Selection of Less-Secure Algorithm During Negotiation ('Algorithm Downgrade')

{"id": "CVE-2026-18691", "cveTags": [], "metrics": {"ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-18691", "role": "CISA Coordinator", "options": [{"exploitation": "none"}, {"automatable": "no"}, {"technicalImpact": "total"}], "version": "2.0.3", "timestamp": "2026-08-11T20:21:49.480663Z"}}], "cvssMetricV31": [{"type": "Secondary", "source": "cna@mongodb.com", "cvssData": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 8.8, "attackVector": "ADJACENT_NETWORK", "baseSeverity": "HIGH", "vectorString": "CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H", "integrityImpact": "HIGH", "userInteraction": "NONE", "attackComplexity": "LOW", "availabilityImpact": "HIGH", "privilegesRequired": "NONE", "confidentialityImpact": "HIGH"}, "impactScore": 5.9, "exploitabilityScore": 2.8}], "cvssMetricV40": [{"type": "Secondary", "source": "cna@mongodb.com", "cvssData": {"Safety": "NOT_DEFINED", "version": "4.0", "Recovery": "NOT_DEFINED", "baseScore": 9.0, "Automatable": "NOT_DEFINED", "attackVector": "ADJACENT", "baseSeverity": "CRITICAL", "valueDensity": "NOT_DEFINED", "vectorString": "CVSS:4.0/AV:A/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X", "exploitMaturity": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED", "userInteraction": "NONE", "attackComplexity": "LOW", "attackRequirements": "PRESENT", "privilegesRequired": "NONE", "subIntegrityImpact": "HIGH", "vulnIntegrityImpact": "HIGH", "integrityRequirement": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "subAvailabilityImpact": "HIGH", "vulnAvailabilityImpact": "HIGH", "availabilityRequirement": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "subConfidentialityImpact": "HIGH", "vulnConfidentialityImpact": "HIGH", "confidentialityRequirement": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED"}}]}, "affected": [{"source": "cna@mongodb.com", "affectedData": [{"vendor": "MongoDB", "product": "MongoDB Server", "versions": [{"status": "affected", "version": "8.3.0", "lessThan": "8.3.8", "versionType": "semver"}, {"status": "affected", "version": "8.0", "lessThan": "8.0.29", "versionType": "semver"}, {"status": "affected", "version": "7.0", "lessThan": "7.0.40", "versionType": "semver"}], "defaultStatus": "unaffected"}]}], "published": "2026-08-11T19:17:22.903", "references": [{"url": "https://jira.mongodb.org/browse/SERVER-130264", "source": "cna@mongodb.com"}], "vulnStatus": "Undergoing Analysis", "weaknesses": [{"type": "Secondary", "source": "cna@mongodb.com", "description": [{"lang": "en", "value": "CWE-757"}]}], "descriptions": [{"lang": "en", "value": "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."}], "lastModified": "2026-08-28T21:16:15.740", "sourceIdentifier": "cna@mongodb.com"}