# CVE-2026-86439 — knowns-dev knowns

> As of 2026-09-08, CVE-2026-86439 is a HIGH-severity vulnerability in knowns-dev knowns, CVSS v3.1 8.8, EPSS 0.7% (52.7th percentile). No Threadlinqs-tracked threat campaign has been attributed to CVE-2026-86439 as of 2026-09-08; the identifier is re-checked against the Threadlinqs threat corpus on every daily ingest.

**Last updated:** 2026-09-08

## What is CVE-2026-86439?

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.

The record classifies CVE-2026-86439 under weakness class [CWE-22](https://intel.threadlinqs.com/cwe/CWE-22). Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs low-privilege credentials, needs no user interaction, and has high impact on confidentiality, integrity, availability. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 28 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 8.8 — HIGH (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **CVSS v4.0 base score:** 8.7 (`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`)
- **EPSS (FIRST):** 0.7% probability of exploitation in the next 30 days, higher than 52.7% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 6.5/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-09-07, last modified 2026-09-08

## Is CVE-2026-86439 being exploited?

It currently carries a trending score of 43 in the Threadlinqs vulnerability feed.

## Affected products and versions

- [knowns-dev](https://intel.threadlinqs.com/vendors/knowns-dev): knowns

## How to fix CVE-2026-86439

No vendor patch reference has been recorded for CVE-2026-86439 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-86439

No threat campaign in the Threadlinqs corpus currently references CVE-2026-86439, in its CVE list or as an indicator. The linkage is recomputed from the live corpus on every daily ingest, so this section fills in as soon as a tracked campaign cites the identifier.

## Sources

Enriched from CVE.org, NVD, GitHub Security Advisories, FIRST EPSS. Last verified by Threadlinqs on 2026-09-08. This product uses the NVD API but is not endorsed or certified by the NVD.

**Vendor advisory and patch**

- [github.com — vendor advisory](https://github.com/knowns-dev/knowns/security/advisories/GHSA-9gfj-28hw-jchp)
- [github.com — patch](https://github.com/knowns-dev/knowns/commit/09c5a96fd5817b941dc86669278c1a17db10ed4e)
- [github.com — release notes](https://github.com/knowns-dev/knowns/releases/tag/v0.30.0)

**Technical analysis**

- [github.com — technical description](https://github.com/knowns-dev/knowns/blob/v0.29.1/internal/storage/doc_store.go#L124-L129)
- [github.com — technical description (memory store)](https://github.com/knowns-dev/knowns/blob/v0.29.1/internal/storage/memory_store.go#L203-L211)

**Third-party advisory**

- [vulncheck.com — third party advisory](https://www.vulncheck.com/advisories/knowns-before-0.30.0-path-traversal-via-mcp-doc-and-memory-tools)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-86439
Full detection coverage and IOCs for threats exploiting CVE-2026-86439 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp