---
id: "CVE-2026-121617"
kind: "vulnerability"
aliases: ["CVE-2026-121617"]
title: "Linksys E5600 router: firmware upload handler lets remote attackers write out of bounds"
severity: "high"
cvss: 7.8
epss: null
exploited: false
status: "open"
category: "infrastructure"
products: [{"name": "E5600", "fixed": [], "affected": "1.1.0.26", "ecosystem": "vendor"}]
ecosystems: []
tags: ["e5600", "home-router", "infrastructure", "iot", "linksys"]
not_affected_if: ["other-models", "unsupported-device-not-used"]
published_at: "2026-11-04T03:17:15+00:00"
first_seen_at: "2026-11-04T03:46:39+00:00"
updated_at: "2026-11-04T03:48:39+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-121617", "first_seen_at": "2026-11-04T03:46:39+00:00"}, {"source": "analyst", "url": null, "first_seen_at": "2026-11-04T03:48:39+00:00"}]
---

# Linksys E5600 router: firmware upload handler lets remote attackers write out of bounds

The Linksys E5600 router's firmware upload CGI handler (/cgi-bin/upload_fw.cgi) has an out-of-bounds write in its multipart header parsing. A remote attacker can send a crafted request to corrupt memory on the device, and a public exploit exists.

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

## Affected

- vendor:E5600 affected 1.1.0.26 fixed ?

## How to check

- Check the router model and firmware version on its admin page; the affected version is `1.1.0.26`.
- Check whether the router's admin interface is reachable from the internet.

## Timeline

- 2026-11-04T03:46:39+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-121617
- 2026-11-04T03:48:39+00:00 analyst — Only NVD (VulDB CNA) found; no Linksys advisory, no fix. 1.1.0.26 is the latest release in Linksys's own notes (Dec 2021), so no newer firmware seen. Auth requirement for upload_fw.cgi NOT confirmed: CVSS vector says PR:N but that is the CNA's claim. PoC link not found. Nothing verified; fix status left unconfirmed since no vendor page says no fix.

## Documents

- [describes] NVD: CVE-2026-121617 https://nvd.nist.gov/vuln/detail/CVE-2026-121617
- [mentions] Linksys E5600 1.1.0.26 release notes (Dec 20, 2021) https://downloads.linksys.com/support/assets/releasenotes/E5600_1.1.0.26_Customer_Release_Notes.txt

## From the sources

A security flaw has been discovered in Linksys E5600 1.1.0.26. Affected by this issue is the function init_multipart of the file /cgi-bin/upload_fw.cgi of the component Header Parser. The manipulation results in out-of-bounds write. The attack may be launched remotely. The exploit has been released to the public and may be used for attacks. The vendor was contacted early about this disclosure but did not respond in any way. This vulnerability only affects products that are no longer supported by the maintainer.

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