PatchSiren

PatchSiren cyber security CVE debrief

CVE-2026-42926 F5 CVE debrief

PatchSiren debrief for CVE-2026-42926, a MEDIUM severity vulnerability in NGINX Open Source. The vulnerability allows an attacker to inject frame headers and payload bytes to the upstream peer when NGINX Open Source is configured to proxy HTTP/2 traffic. This can occur when proxy_http_version is set to 2 and proxy_set_body is used. Users of NGINX Open Source configured to proxy HTTP/2 traffic should be aware of this vulnerability and take necessary actions.

Vendor
F5
Product
NGINX Open Source
CVSS
MEDIUM 6.3
CISA KEV
Not listed in stored evidence
Original CVE published
2026-05-13
Original CVE updated
2026-06-18
Advisory published
2026-05-13
Advisory updated
2026-06-18

Who should care

Users of NGINX Open Source configured to proxy HTTP/2 traffic should be aware of this vulnerability. This includes operators, platform administrators, vulnerability management teams, and security teams who need to assess the impact on their deployments and take necessary actions.

Technical summary

CVE-2026-42926 is a vulnerability in NGINX Open Source when configured to proxy HTTP/2 traffic by setting proxy_http_version to 2 and using proxy_set_body. An attacker may inject frame headers and payload bytes to the upstream peer. This vulnerability has a CVSS score of 6.3 and is classified as MEDIUM severity. Affected users should review their configurations and apply patches or recommended mitigations.

Defensive priority

Apply vendor patches or recommended mitigations.

Recommended defensive actions

  • Apply NGINX Open Source patches or updates.
  • Review and adjust proxy configurations.
  • Monitor for suspicious traffic patterns.
  • 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

Vendor advisory and CVE details indicate potential for frame header and payload injection. Affected deployments should verify configurations and monitor for suspicious traffic. The vulnerability is MEDIUM severity and affects NGINX Open Source when configured to proxy HTTP/2 traffic. Users should review official advisories and apply patches or mitigations as recommended.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-42926 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-42926

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-42926 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-42926

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.