NGINX: Forged SSL sessions allow client certificate bypass

Summary

NGINX Plus and NGINX Open Source are affected when ssl_session_cache shared is configured without an explicit ssl_session_ticket_key file, so session ticket keys rotate automatically. A remote, unauthenticated attacker can forge client SSL sessions in a non-deterministic way that they cannot control. This can be used to bypass client certificate verification and may expose resources or information to unintended actors. The issue affects the data plane only.

Affected

• NGINX Open Source 1.30.0 to before 1.30.6
• NGINX Open Source 1.31.0 to before 1.31.7
• NGINX Open Source 1.23.3 and later, no fixed version listed by F5
• NGINX Plus 37.0.0 to before 37.0.5.1
• NGINX Plus 37.1.0 to before 37.1.0.1
• NGINX Plus R33 to R36, no fixed version listed by F5
• Versions past End of Technical Support are not evaluated

Fixed in

• NGINX Open Source 1.30.6 and 1.31.7
• NGINX Plus 37.0.5.1 and 37.1.0.1
• Other nginx-based builds: apply your vendor's update

Workaround

• Do not enable automatic rotation of SSL session ticket keys.
• Remove the ssl_session_cache shared directive, or load static keys from a file with ssl_session_ticket_key.
• Servers with ssl_session_tickets off are not affected.

Exploitation

• A public proof of concept has been published by the finder.
• No exploitation in the wild is known.
• CISA SSVC: exploitation none, not automatable, partial technical impact.
• EPSS is very low (0.00175).

Our recommendation

• Identify all NGINX instances, including appliances and ingress controllers built on nginx.
• Update to a fixed version listed above or apply your vendor's build.
• Until patched, check for ssl_session_cache shared without ssl_session_ticket_key (for example with nginx -T) and apply a workaround.
• Prioritise servers that use client certificate (mTLS) authentication.

Public exploits iAttack code is publicly available (PoC on GitHub, Metasploit or Exploit-DB).

Links to third-party sites, not checked by us – exploit code can contain malware. Only use it in isolated test environments.

• Proof of concept on GitHub (1 repositories) iAttack code is publicly available (PoC on GitHub, Metasploit or Exploit-DB).
  PhiNode-Labs/nginx-cve-2026-97629

Research sources

• F5 advisory K000162606 my.f5.com
• OSV/Bitnami entry BIT-nginx-2026-97629 osv.dev
• HeroDevs NGINX release notes docs.herodevs.com
• OpenBSD ports update to nginx 1.30.6 www.mail-archive.com
• Red Hat RHSA-2026:83427 via Vulners vulners.com

Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 1 Nov 2026, 13:45.