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CVE-2026-84970

Heap over-read or silent misparse via 32-bit truncation of JSON length in BSON JSON parser

5.9 MediumFix available

A numeric truncation weakness exists in the JSON parsing component of the MongoDB C++ Driver's BSON library. An actor who controls the text that an embedding application hands to the library's public JSON parsing interface, when that text is very large, can cause the library to read memory beyond the supplied buffer and return it to the caller, to silently accept only part of the input as a complete document, or to terminate the process. No MongoDB server, credentials, or non-default configuration is required; the effect is confined to the process that uses the library.

Attack profile

How easy it is to exploit

Attack vector
Local
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
Low
Integrity
Low
Availability
High

Exploit likelihood

0.12%Unchanged since Sep 4, 2026
90%50%10%1%

What each source reports

CVE List Score used 5.9

Heap over-read or silent misparse via 32-bit truncation of JSON length in BSON JSON parser

A numeric truncation weakness exists in the JSON parsing component of the MongoDB C++ Driver's BSON library. An actor who controls the text that an embedding application hands to the library's public JSON parsing interface, when that text is very large, can cause the library to read memory beyond the supplied buffer and return it to the caller, to silently accept only part of the input as a complete document, or to terminate the process. No MongoDB server, credentials, or non-default configuration is required; the effect is confined to the process that uses the library.

Record
CVE-2026-84970
CVSS 4.0
5.9 MediumCVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N
CVSS 3.1
6.2 MediumCVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
Weakness
CWE-681
Updated
2026-11-02
EUVDEUVD-2026-70505 5.9

A numeric truncation weakness exists in the JSON parsing component of the MongoDB C++ Driver's BSON library. An actor who controls the text that an embedding application hands to the library's public JSON parsing interface, when that text is very large, can cause the library to read memory beyond the supplied buffer and return it to the caller, to silently accept only part of the input as a complete document, or to terminate the process. No MongoDB server, credentials, or non-default configuration is required; the effect is confined to the process that uses the library.

Record
EUVD-2026-70505
CVSS 4.0
5.9 MediumCVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N
Updated
2026-11-02
GitHub AdvisoriesGHSA-j94p-2ppx-483m 5.9

A numeric truncation weakness exists in the JSON parsing component of the MongoDB C++ Driver's...

A numeric truncation weakness exists in the JSON parsing component of the MongoDB C++ Driver's BSON library. An actor who controls the text that an embedding application hands to the library's public JSON parsing interface, when that text is very large, can cause the library to read memory beyond the supplied buffer and return it to the caller, to silently accept only part of the input as a complete document, or to terminate the process. No MongoDB server, credentials, or non-default configuration is required; the effect is confined to the process that uses the library.

Record
GHSA-j94p-2ppx-483m
CVSS 4.0
5.9 MediumCVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:H/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
CVSS 3.1
6.2 MediumCVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
Weakness
CWE-681
Updated
2026-11-02
NVD 5.9

A numeric truncation weakness exists in the JSON parsing component of the MongoDB C++ Driver's BSON library. An actor who controls the text that an embedding application hands to the library's public JSON parsing interface, when that text is very large, can cause the library to read memory beyond the supplied buffer and return it to the caller, to silently accept only part of the input as a complete document, or to terminate the process. No MongoDB server, credentials, or non-default configuration is required; the effect is confined to the process that uses the library.

Record
CVE-2026-84970
CVSS 4.0
5.9 MediumCVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:H/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
CVSS 3.1
6.2 MediumCVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
CVSS 3.1
5.8 MediumCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
Weakness
CWE-681
Updated
2026-11-02
OSV 5.9

Heap over-read or silent misparse via 32-bit truncation of JSON length in BSON JSON parser

A numeric truncation weakness exists in the JSON parsing component of the MongoDB C++ Driver's BSON library. An actor who controls the text that an embedding application hands to the library's public JSON parsing interface, when that text is very large, can cause the library to read memory beyond the supplied buffer and return it to the caller, to silently accept only part of the input as a complete document, or to terminate the process. No MongoDB server, credentials, or non-default configuration is required; the effect is confined to the process that uses the library.

Record
CVE-2026-84970
CVSS 4.0
5.9 MediumCVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N
Weakness
CWE-681
Updated
2026-11-02
OSVDEBIAN-CVE-2026-84970 5.8

A numeric truncation weakness exists in the JSON parsing component of the MongoDB C++ Driver's BSON library. An actor who controls the text that an embedding application hands to the library's public JSON parsing interface, when that text is very large, can cause the library to read memory beyond the supplied buffer and return it to the caller, to silently accept only part of the input as a complete document, or to terminate the process. No MongoDB server, credentials, or non-default configuration is required; the effect is confined to the process that uses the library.

Record
DEBIAN-CVE-2026-84970
CVSS 3.1
5.8 MediumCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
Updated
2026-11-02
OSVUBUNTU-CVE-2026-84970 5.9

A numeric truncation weakness exists in the JSON parsing component of the MongoDB C++ Driver's BSON library. An actor who controls the text that an embedding application hands to the library's public JSON parsing interface, when that text is very large, can cause the library to read memory beyond the supplied buffer and return it to the caller, to silently accept only part of the input as a complete document, or to terminate the process. No MongoDB server, credentials, or non-default configuration is required; the effect is confined to the process that uses the library.

Record
UBUNTU-CVE-2026-84970
CVSS 4.0
5.9 MediumCVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N
CVSS 3.1
5.8 MediumCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
CVSS 3.1
6.2 MediumCVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
mongo-cxx-driver
Debian:14
before 4.5.2-1, plus listed versions
3.10.1-13.10.2-13.11.0-13.4.1-13.6.0-1
Show 16 moreShow less
3.6.1-13.6.2-13.6.3-13.6.5-13.6.6-13.6.7-13.7.0-13.7.1-13.8.0-13.8.1-13.9.0-14.0.0-14.1.4-14.4.0-14.5.0-14.5.1-1
4.5.2-1
mongo-cxx-driver
Ubuntu:26.10
All versions, plus listed versions
4.4.0-14.5.0-1
None known

History

History
RecordedChangedSources
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-84970 is a medium vulnerability (CVSS 5.9) in Mongodb C++ Driver, published September 3, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.12%, the 2nd percentile. Fixed in mongo-cxx-driver 4.5.2-1.

References

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