CVE-2026-126839
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.
INFO
Published Date :
Nov. 13, 2026, 12:20 a.m.
Last Modified :
Nov. 13, 2026, 12:20 a.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | MEDIUM | a39b4221-9bd0-4244-95fc-f3e2e07f1deb | ||||
| CVSS 3.1 | MEDIUM | MITRE-CVE | ||||
| CVSS 3.1 | MEDIUM | [email protected] | ||||
| CVSS 4.0 | LOW | a39b4221-9bd0-4244-95fc-f3e2e07f1deb | ||||
| CVSS 4.0 | LOW | [email protected] |
Solution
- Update the component to precisely identify types.
- Avoid deserializing untrusted data.
- Use explicit type allow-lists.
- Validate deserialized object states.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-126839.
| URL | Resource |
|---|---|
| https://jira.mongodb.org/browse/CSHARP-6169 |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-126839 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-126839
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-126839 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-126839 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
New CVE Received by [email protected]
Nov. 13, 2026
Action Type Old Value New Value 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. Added CVSS V4.0 AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N/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 Added CVSS V3.1 AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L Added CWE CWE-502 Added Affected New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/126xxx/CVE-2026-126839.json">CVE-2026-126839</a> Added Reference https://jira.mongodb.org/browse/CSHARP-6169