CVE-2026-126839: Deserialization allow-list bypass via anonymous-type misdetection in BSON object deserialization
MongoDB · C# Driver
Vendor fix available · Affected: MongoDB C# Driver · Exploitation: unlikely (under 1%)
Not in CyberSIXT coverage yet: no article names this CVE. This page shows the public record.
Higher than 7% of scored CVEs
DescriptionCVE.org
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 products1
From the CVE record. A product or version that is not listed is unknown, not unaffected.
- MongoDB · C# Driverfrom 2.21.0 before 3.14.0
On the Atlas
Every published CVE is on the CyberSIXT Atlas, grouped by weakness, vendor and month.
- Exploitation
- Unlikely (under 1%). EPSS under 1%, or no score yet.
- CISA KEV
- Not listed
- Public check
- No public nuclei template
- Vendor
- MongoDB
- Published
- November 2026
CoverageNo articles yet
No CyberSIXT article names CVE-2026-126839 yet, so there is no coverage timeline, action brief or change log for it. Everything on this page comes from the public CVE record, CISA KEV, EPSS and the nuclei template index. Search the archive or see the CVEs in the news.