# CVE-2026-121617: Linksys E5600 Header upload_fw.cgi init_multipart out-of-bounds write

- Exploited (CISA KEV): no
- Published: 2026-11-04
- CVSS: 8.7 HIGH (v4.0)
- EPSS: no score
- CWE: CWE-787, CWE-119

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.

## Edge WAF coverage (claimed by vendors, not measured)

| Vendor | Status | First rule | Days after publication |
|---|---|---|---|
| Cloudflare | No public claim | — | — |
| AWS | No public claim | — | — |
| Microsoft Azure | No public claim | — | — |
| Google Cloud | No public claim | — | — |
| Fastly | No public claim | — | — |
| Vercel | No public claim | — | — |
| F5 | No public claim | — | — |
| Akamai | No public source | — | — |
| OWASP CRS | No public claim | — | — |

## Social

3 posts seen since 2026-11-04.

- bluesky 2026-11-04: 🟠 CVE-2026-121617 - High (7.5)  A security flaw has been discovered in Linksys E5600 1.1.0.26. Affected by this issue is the func...  https://www.thehackerwire.com/vulnerability/CVE-2026-121617/  #infosec #cybersecurity #CVE #vulnerability #security #patchstack (https://bsky.app/profile/thehackerwire.bsky.social/post/3mzhnp7pfri25)
- mastodon 2026-11-04: 🟠 CVE-2026-121617 - High (7.5) 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… (https://mastodon.social/@thehackerwire/117556591541875793)
- bluesky 2026-11-04: CVE-2026-121617 - Linksys E5600 Header upload_fw.cgi init_multipart out-of-bounds write CVE ID : CVE-2026-121617    Published : Nov. 4, 2026, 2:45 a.m. \| 19 minutes ago    Description : A security flaw has been discovered in Linksys E5600 1.1.0.26. Affected by this issue is th... (https://bsky.app/profile/cve.skyfleet.blue/post/indcpamfwwb5e)

"No public claim" means no vendor statement names this CVE; "Before feed history" means the CVE is older than the vendor feed. In both cases generic rules may still block it.

HTML: https://cve.vigilbase.com/cve/CVE-2026-121617 · JSON: https://cve.vigilbase.com/api/v1/cves/CVE-2026-121617