CVE-2026-126839

Deserialization allow-list bypass via anonymous-type misdetection in BSON object deserialization

Published Nov 12, 2026 CVSS 4.0 · 2.3 Low EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

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History
Type Values Removed Values Added
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.
Title Deserialization allow-list bypass via anonymous-type misdetection in BSON object deserialization
Weaknesses CWE-502
References
Metrics cvssV3_1

{'score': 4.2, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L'}

cvssV4_0

{'score': 2.3, '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'}

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Weaknesses

Sources

Status
PUBLISHED
Assigner
mongodb
Published
Updated
Nov 12, 2026, 11:58 PM
Reserved
Nov 11, 2026, 10:04 PM
Status
Received
Published
Nov 13, 2026, 12:20 AM
Modified
Nov 13, 2026, 12:20 AM