{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-126839", "assignerOrgId": "a39b4221-9bd0-4244-95fc-f3e2e07f1deb", "state": "PUBLISHED", "assignerShortName": "mongodb", "dateReserved": "2026-11-11T22:04:48.453Z", "datePublished": "2026-11-12T23:58:16.490Z", "dateUpdated": "2026-11-12T23:58:16.490Z"}, "containers": {"cna": {"providerMetadata": {"orgId": "a39b4221-9bd0-4244-95fc-f3e2e07f1deb", "shortName": "mongodb", "dateUpdated": "2026-11-12T23:58:16.490Z"}, "title": "Deserialization allow-list bypass via anonymous-type misdetection in BSON object deserialization", "problemTypes": [{"descriptions": [{"lang": "en", "cweId": "CWE-502", "description": "CWE-502: Deserialization of Untrusted Data", "type": "CWE"}]}], "affected": [{"vendor": "MongoDB", "product": "C# Driver", "versions": [{"status": "affected", "version": "2.21.0", "lessThan": "3.14.0", "versionType": "semver"}], "defaultStatus": "unaffected"}], "descriptions": [{"lang": "en", "value": "A deserialization type-restriction control in the BSON serialization component can be bypassed because the check used to recognize a class of compiler-generated types relies on an overly permissive heuristic rather than a precise identification. An unauthorized party able to supply BSON content that an application later deserializes into a loosely typed member can cause types outside the intended allow-list to be constructed and populated with unauthorized party-supplied values inside the consuming application. This can lead to unexpected object state and errors in downstream application logic. No elevated privileges beyond the ability to place unauthorized party-influenced content in the deserialization path are required.", "supportingMedia": [{"type": "text/html", "base64": false, "value": "A deserialization type-restriction control in the BSON serialization component can be bypassed because the check used to recognize a class of compiler-generated types relies on an overly permissive heuristic rather than a precise identification. An unauthorized party able to supply BSON content that an application later deserializes into a loosely typed member can cause types outside the intended allow-list to be constructed and populated with unauthorized party-supplied values inside the consuming application. This can lead to unexpected object state and errors in downstream application logic. No elevated privileges beyond the ability to place unauthorized party-influenced content in the deserialization path are required."}]}], "references": [{"url": "https://jira.mongodb.org/browse/CSHARP-6169"}], "metrics": [{"format": "CVSS", "scenarios": [{"lang": "en", "value": "GENERAL"}], "cvssV4_0": {"attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "PRESENT", "privilegesRequired": "LOW", "userInteraction": "NONE", "vulnConfidentialityImpact": "NONE", "subConfidentialityImpact": "NONE", "vulnIntegrityImpact": "LOW", "subIntegrityImpact": "NONE", "vulnAvailabilityImpact": "LOW", "subAvailabilityImpact": "NONE", "exploitMaturity": "NOT_DEFINED", "Safety": "NOT_DEFINED", "Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED", "version": "4.0", "baseSeverity": "LOW", "baseScore": 2.3, "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N"}}, {"format": "CVSS", "scenarios": [{"lang": "en", "value": "GENERAL"}], "cvssV3_1": {"version": "3.1", "attackVector": "NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "LOW", "availabilityImpact": "LOW", "baseSeverity": "MEDIUM", "baseScore": 4.2, "vectorString": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L"}}], "source": {"discovery": "UNKNOWN"}, "x_generator": {"engine": "Vulnogram 1.0.5"}}}}

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