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HighVulnerabilityCVE-2026-97629updated 26 Oct 2026, 17:26 UTC

nginx web server: flaw lets attackers forge TLS sessions and bypass client certificate checks

nginx is a widely used web server. This flaw can let an attacker pretend to be a trusted client and get past certificate-based login checks, and it may also let them crash the server.

Fix availableOfficial, 2 sources
SeverityHighVulnerability
Being exploited?UnclearNo reports either way yet
Fix available?YesFixed nginx packages are provided in Debian DSA-6575-1 and Ubuntu USN-8955-1. Specific fixed version numbers: unknown. · since 26 Oct 2026
How sure is this?Official, 2 sourcesBacked by an official source

How the attack works simplified

  1. 1Attacker connectsSends crafted TLS session requests
  2. 2Worker uses bad keyUninitialised ticket key material is used
  3. 3Session forgedAttacker creates a valid-looking TLS session
  4. 4Access gainedClient certificate check is bypassed
  5. ResultAttacker bypasses client certificate authentication

What happened

CVE-2026-97629 is an incomplete synchronisation of TLS session ticket keys between nginx worker processes, so a worker can use uninitialised key material to forge TLS sessions and bypass client certificate authentication. It is one of several nginx flaws in the same advisory set (CVE-2026-15176, CVE-2026-93479, CVE-2026-95101, CVE-2026-97205) that can cause memory corruption, denial of service, or request injection.

Why it is dangerous: Servers that rely on client certificates to restrict access could let unauthorised clients in, and crashes or request injection could affect availability and backend services.

Are you affected?

You are affected if you run nginx with a shared session cache and without explicit TLS session ticket key rotation, on Ubuntu 24.04 LTS, Ubuntu 26.04 LTS, or Ubuntu 26.10, or on affected Debian trixie packages.

nginx packages in Debian trixie (affected by DSA-6575-1) and Ubuntu 24.04 LTS, 26.04 LTS, 26.10 (USN-8955-1). Exact vulnerable version numbers: unknown.

What to do

  1. Update nginx to the fixed package from Debian DSA-6575-1 or Ubuntu USN-8955-1 and restart it
  2. If you cannot update at once, configure explicit TLS session ticket key rotation
  3. Review any services that depend on client certificate authentication

Timeline

  1. 21 Oct 2026, 00:00 UTC
    Publicly disclosed
  2. 21 Oct 2026, 00:00 UTC
    Reported by Debian DSA · Debian DSA
  3. 26 Oct 2026, 17:26 UTC
    Ubuntu Security reported on it · Ubuntu Security

Sources 2 reports, oldest first

Official vendor, government CERT or advisory database

Technical details

ID
CVE-2026-97629
EPSS
0.2% chance of exploitation within 30 days
Disclosed
21 Oct 2026, 00:00 UTC
On Zero Radar
before the radar started
Last change
26 Oct 2026, 17:26 UTC

The plain-language parts and the attack diagram were written by an AI model (anthropic/claude-haiku-5.5) from the sources above. Facts like versions, exploitation and dates come from the sources themselves. How Zero Radar works

nginx web server: flaw lets attackers forge TLS sessions and bypass client certificate checks · Zero Radar