{"id":"CVE-2026-126839","state":"PUBLISHED","title":"Deserialization allow-list bypass via anonymous-type misdetection in BSON object deserialization","description":"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.","publishedAt":"2026-11-12T23:58:16.490Z","updatedAt":"2026-11-12T23:58:16.490Z","severity":{"score":2.3,"label":"Low","version":"4.0","vector":"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","source":"mongodb"},"assigner":"mongodb","products":["MongoDB C# Driver"],"affected":[{"vendor":"MongoDB","product":"C# Driver","defaultStatus":"unaffected","versions":[{"version":"2.21.0","status":"affected","lessThan":"3.14.0","versionType":"semver"}]}],"references":["https://jira.mongodb.org/browse/CSHARP-6169"],"weaknesses":["CWE-502"],"ingestedAt":"2026-11-13T00:04:07.093Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/126xxx/CVE-2026-126839.json","commit":"b11ebad141cb1342d2d59e57e49d50b8dd082cf9","baselineCommit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-126839","state":"PUBLISHED","datePublished":"2026-11-12T23:58:16.490Z","dateUpdated":"2026-11-12T23:58:16.490Z","assignerShortName":"mongodb","assignerOrgId":"a39b4221-9bd0-4244-95fc-f3e2e07f1deb","dateReserved":"2026-11-11T22:04:48.453Z"},"containers":{"cna":{"title":"Deserialization allow-list bypass via anonymous-type misdetection in BSON object deserialization","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."}],"affected":[{"vendor":"MongoDB","product":"C# Driver","defaultStatus":"unaffected","versions":[{"version":"2.21.0","status":"affected","lessThan":"3.14.0","versionType":"semver"}]}],"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"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-502","lang":"en","description":"CWE-502: Deserialization of Untrusted Data","type":"CWE"}]}],"providerMetadata":{"shortName":"mongodb","orgId":"a39b4221-9bd0-4244-95fc-f3e2e07f1deb","dateUpdated":"2026-11-12T23:58:16.490Z"},"source":{"discovery":"UNKNOWN"},"x_generator":{"engine":"Vulnogram 1.0.5"}}}}}