---
id: "CVE-2021-20090"
kind: "vulnerability"
aliases: ["CVE-2021-20090"]
title: "Arcadyan Buffalo Firmware: Arcadyan Buffalo Firmware Path Traversal Vulnerability"
severity: "critical"
cvss: 9.8
epss: 0.99982
exploited: true
status: "open"
category: "infrastructure"
products: [{"name": "Arcadyan Buffalo Firmware", "fixed": [], "affected": "", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["arcadyan", "buffalo", "exploited", "infrastructure", "routers", "self-hosted"]
not_affected_if: ["unknown"]
published_at: "2021-04-29T15:15:10+00:00"
first_seen_at: "2026-10-23T19:11:53+00:00"
updated_at: "2026-10-23T21:57:35+00:00"
sources: [{"source": "kev", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-20090", "first_seen_at": "2026-10-23T19:11:53+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2021-20090", "first_seen_at": "2026-10-23T19:13:44+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2021-20090", "first_seen_at": "2026-10-23T21:57:35+00:00"}]
---

# Arcadyan Buffalo Firmware: Arcadyan Buffalo Firmware Path Traversal Vulnerability

Arcadyan Buffalo router firmware has a path traversal flaw that lets remote attackers bypass authentication and read sensitive information. CISA lists it as actively exploited in the wild.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:Arcadyan Buffalo Firmware affected ? fixed ?

## Fix

Apply firmware updates per vendor instructions, as CISA directs; the specific fixed versions are unknown from the sources.

## Timeline

- 2026-10-23T19:11:53+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-20090
- 2026-10-23T19:13:44+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2021-20090
- 2026-10-23T21:57:35+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2021-20090

## From the sources

Arcadyan Buffalo firmware contains a path traversal vulnerability that could allow unauthenticated, remote attackers to bypass authentication and access sensitive information. This vulnerability affects multiple routers across several different vendors.

CISA required action: Apply updates per vendor instructions.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_