# CVE-2026-86439

## Summary

- **CVE ID:** CVE-2026-86439
- **Severity:** HIGH
- **CVSS Score:** 8.8 (CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N)
- **CWE:** CWE-22
- **Published:** Sep 7, 2026
- **Last Modified:** Sep 11, 2026

## Description

knowns versions before 0.30.0 fail to validate filesystem paths in MCP tool arguments, allowing attackers to read, create, overwrite and delete files outside the project directory. Attackers can supply path arguments containing directory traversal sequences to access arbitrary Markdown files accessible to the server process.

## Affected Products

- knowns-dev — knowns (0)
- knowns-dev — knowns (0.30.0)

## References

- [CNA](https://github.com/knowns-dev/knowns/security/advisories/GHSA-9gfj-28hw-jchp)
- [CNA](https://github.com/knowns-dev/knowns/blob/v0.29.1/internal/storage/doc_store.go#L124-L129)
- [CNA](https://github.com/knowns-dev/knowns/blob/v0.29.1/internal/storage/memory_store.go#L203-L211)
- [CNA](https://github.com/knowns-dev/knowns/commit/09c5a96fd5817b941dc86669278c1a17db10ed4e)
- [CNA](https://github.com/knowns-dev/knowns/releases/tag/v0.30.0)
- [CNA](https://www.vulncheck.com/advisories/knowns-before-0.30.0-path-traversal-via-mcp-doc-and-memory-tools)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.75%
- **EPSS Percentile:** 53.3

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-17._