MediumCVE-2026-106435

Application denial of service via out-of-bounds read in BSON Regex decoding in MongoDB Python Driver (CVE-2026-106435)

Published 08.10.2026Last modified 15.10.2026Sources: BSI, OSV, Hersteller, CVE.org

What is affected, what to do

Update python_driver to version 4.18.3, pymongo to version 4.18.3.

Affected: MongoDB Python Driver lte 0.10.3..4.18.2

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Metrics

5.9

Priority

XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

Source: Vendor (CNA), CVSS v4

5.1

CVSS v3

Severity Medium on the scale from 0 to 10.

Source: BSI, OSV, Hersteller, CVE.org

0.1 %

EPSS score

Low — model estimates < 1% exploitation likelihood.

Source: FIRST EPSS, percentile 0.6

Show all metrics

Severity: Medium
Priority (0–325) The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first? Read in glossary: 59.50 Methodology
Exploit maturity An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack. Read in glossary: no public PoC known
XIEM Effective CVSS XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command. Read in glossary: 5.9 Methodology
CVSS v3 CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions. Read in glossary: 5.1
CVSS v4 CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions. Read in glossary: 5.9
EPSS score The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“. Read in glossary: 0.1 %; Low — model estimates < 1% exploitation likelihood.
EPSS percentile The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking. Read in glossary: 0.6; Low — this CVE sits in the lower 10% of all CVEs scored today.
KEV status The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching. Read in glossary: —
Published: 08.10.2026
CWE CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect. Read in glossary: CWE-125

Detection rules

No NEOSEC detection rule is available for this vulnerability yet.

Classification under NIS2 and CRA

Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

NIS2 NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management. Read in glossary: Handle the vulnerability in regular vulnerability handling under Art. 21(2)(e) NIS2.
CRA The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates. Read in glossary: From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
ISO/IEC 27001 ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security. Read in glossary: Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

Description

Impact

The C extension's BSON decoder scans a Regex element's pattern and flags strings with strlen before checking the document's remaining length, so a crafted truncated Regex element can read past the end of the caller's buffer. bson.decode and bson.decode_all accept mmap and array buffers, which carry no NUL sentinel; the read can cross into unmapped memory and kill the process with an uncatchable SIGSEGV. Any application decoding untrusted BSON from such buffers is affected — impact is availability only, since the out-of-bounds bytes are never returned as content. NUL-terminated buffers (bytes, bytearray) raise InvalidBSON at worst; the driver's own transport and pure-Python installs are not affected. All releases through 4.18.2 are affected when the C extension is loaded.

Patches

Fixed in PyMongo 4.18.3. Malformed Regex elements now raise InvalidBSON on every accepted buffer type; valid documents decode unchanged.

Workarounds

Decode untrusted BSON only from NUL-terminated buffers — bytes or bytearray — and copy mmap input first, e.g. bytes(mm[:size]).

Source: BSI WID Portal, BSI CSAF, OSV (Open Source Vulnerabilities), GitHub Security Advisories, NVD (NIST), cvelistv5

Affected products

The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

Affected products
		Affected versions	Fixed in
MongoDB	Python Driver	`0.10.3 – ≤ 4.18.2`	—
mongodb	python_driver	`< 4.18.3`	`4.18.3`
Open Source	MongoDB	`Go Driver` `PHP Driver` `Python Driver` `C Driver` `libmongocrypt` `C++ Driver`	— — — — — —
pip	pymongo	`>= 3.9.0, <= 4.18.2`	`4.18.3`
pypi	pymongo	`4.4.1` `4.16.0.dev0` `3.9.0` `3.12.3` `4.15.2` `4.18.2` `3.12.2` `3.10.0` `4.5.0` `4.9.1` `4.13.1` `3.11.1` `4.18.0` `4.12.0` `3.11.4` `4.6.3` `4.14.0` `4.3.2` `4.1.1` `4.13.0` `4.14.1` `4.11.3` `4.7.0` `4.10.1` `4.0` `4.15.3` `4.13.2` `4.12.1` `3.12.0` `4.4.0b0` `4.15.5` `4.9.2` `4.11.1` `4.6.2` `4.0.1` `3.10.1` `4.7.1` `3.11.2` `4.17.0`	— — `4.18.3` — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — —

Vendors and products

Weakness classes (CWE)

CWE-125Out-of-bounds Read
Base
The product reads data past the end, or before the beginning, of the intended buffer.
Entry at MITRE CWE-125

References & sources

jira.mongodb.orgbrowse/PYTHON-6110web
github.commongodb/mongo-python-driver/security/advisories/GHSA-98qm-wvgf-…web
NVD (NIST)vuln/detail/CVE-2026-106435advisory
github.commongodb/mongo-python-driver/pull/3109web
github.commongodb/mongo-python-driver/commit/bb8d4e195275e75bd94ebeffb53c…web
github.commongodb/mongo-python-driverpackage
github.commongodb/mongo-python-driver/releases/tag/4.18.3web

Changes to this CVE

Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

15.10.2026Initial analysis by NVDNVD

Newly listed as affected:

MongoDB Python Driver (before 4.18.3)

CVSS V3.1: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H

New references:

https://jira.mongodb.org/browse/PYTHON-6110

Show 3 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
CVSS	added	—	AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
Product configuration	added	—	OR cpe:2.3:a:mongodb:python_driver::::::mongodb:: versions up to (excluding) 4.18.3
Reference type	added	—	MongoDB, Inc.: https://jira.mongodb.org/browse/PYTHON-6110 Types: Vendor Advisory

Source identifier: nvd@nist.gov

09.10.2026Record modifiedCISA ADP

CISA assessment (SSVC): exploitation: none known, automatable: no

Show the original change

Individual changes of this event as published by NVD
Type	Action	Before	After
SSVC assessment	added	—	{"id":"CVE-2026-106435","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-10-09T11:49:15.521416Z"}

Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

08.10.2026ReceivedMongoDB

CVSS V4.0: AV:L/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

CVSS V3.1: AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Weakness type: CWE-125

Description added or changed

New references:

https://jira.mongodb.org/browse/PYTHON-6110

Show 6 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Description	added	—	The MongoDB Python Driver's binary accelerator can read outside a buffer when an application decodes malformed BSON containing a truncated regular-expression element without a trailing NUL byte. An actor who can supply BSON to the documented decode or decode_all API can cause the application process to terminate when the C extension is loaded. The driver's normal database wire-protocol path does not reach this code.
CVSS	added	—	AV:L/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/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	added	—	AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness type (CWE)	added	—	CWE-125
Affected versions (publisher)	added	—	New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/106xxx/CVE-2026-106435.json">CVE-2026-106435</a>
Reference	added	—	https://jira.mongodb.org/browse/PYTHON-6110

Source identifier: cna@mongodb.com

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