PatchSiren cyber security CVE debrief
CVE-2026-56746 netty CVE debrief
CVE-2026-56746 is a security control bypass vulnerability in Netty, a network application framework. The issue affects versions 4.2.0.Final through 4.2.15.Final and 4.1.0.Final through 4.1.135.Final. The vulnerability occurs in the CorsHandler's origin evaluation process, allowing an attacker to bypass security controls by sending a request with an Origin: null header. This bypasses the short-circuit mechanism designed to reject unauthorized cross-origin requests immediately. The issue is fixed in versions 4.1.136.Final and 4.2.16.Final. Users of affected versions should be aware of this vulnerability and take steps to upgrade to a patched version.
- Vendor
- netty
- Product
- Unknown
- CVSS
- MEDIUM 6.5
- CISA KEV
- Not listed in stored evidence
- Original CVE published
- 2026-07-21
- Original CVE updated
- 2026-07-22
- Advisory published
- 2026-07-21
- Advisory updated
- 2026-07-22
Who should care
Users of Netty versions 4.2.0.Final through 4.2.15.Final and 4.1.0.Final through 4.1.135.Final should be aware of this vulnerability and take steps to upgrade to a patched version. This includes operators, platform administrators, vulnerability management teams, and security teams who manage or use Netty in their applications.
Technical summary
The vulnerability is caused by a logical operator error in the origin evaluation process of the CorsHandler in Netty versions 4.2.0.Final through 4.2.15.Final and 4.1.0.Final through 4.1.135.Final. This allows an attacker to bypass the short-circuit mechanism by sending a request with an Origin: null header, forwarding unauthorized requests to the backend application and bypassing intended access controls. The issue is fixed in versions 4.1.136.Final and 4.2.16.Final. Affected users should review their deployments and upgrade to a patched version.
Defensive priority
Medium priority given the CVSS score of 6.5 and the potential for unauthorized access.
Recommended defensive actions
- Upgrade to Netty version 4.1.136.Final or 4.2.16.Final
- Review and update affected applications to use patched Netty versions
- Monitor for suspicious cross-origin requests
- Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.
- Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance.
- Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed.
- Check relevant monitoring, detection, and logs for exposed assets that need extra review.
Evidence notes
Evidence is based on official CVE and NVD records, as well as source references from GitHub. The CVE record was published on 2026-07-21T22:17:14.667Z and last modified on 2026-07-22T20:35:40.827Z. The NVD entry is currently Awaiting Analysis. Limited source detail is available; defenders should verify affected scope and vendor guidance.
Official resources
AI-assisted PatchSiren debrief based on the supplied source corpus. The CVE record was published on 2026-07-21T22:17:14.667Z and has not been modified since then. The NVD entry is currently Awaiting Analysis.