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CVE-2026-121617HIGH · CVSS 7.5

CVE-2026-121617

What's the vulnerability?

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.

R4IM analyst take

Business impact & how R4IM helps

This advisory is on our active-exploitation watchlist. Attackers are using it for initial access, privilege escalation or lateral movement in real-world intrusions. R4IM's offensive security and SOC teams already have detections, exploit replicas and remediation playbooks for this issue.

Validate your exposure

Targeted vulnerability assessment to confirm which of your assets are actually exploitable — not just theoretically affected.

Prove it with a pentest

Our pentesters chain this CVE into realistic attack paths so you see business impact, not just a scan finding.

Web app security testing

If the affected product is internet-facing, our AppSec team will harden it against this and related OWASP-class issues.

24/7 SOC & detection

Continuous monitoring with custom detections for this CVE deployed across your endpoints, identity and cloud.

Talk to a security engineer →

Recommended remediation

  1. Inventory all assets running the affected vendor and product, including shadow IT and third-party hosted instances.
  2. Apply the vendor patch or mitigation referenced in the advisories below. Where no patch exists, isolate the asset or restrict network exposure.
  3. Hunt for indicators of prior compromise — exploitation of this class of bug often predates public disclosure.
  4. Deploy detections for the exploit primitives (network signature, EDR rule, WAF rule) and re-test after remediation.

Need help executing these steps? Our team typically completes validation and remediation within a single patch cycle. Request remediation support →

Vendor & research references