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CVE-2026-26999 traefik CVE debrief

CVE-2026-26999 is a high-severity vulnerability in Traefik, an HTTP reverse proxy and load balancer. The vulnerability allows an attacker to cause a denial of service by sending an incomplete TLS record, which can stall the TLS handshake indefinitely, leading to a resource exhaustion. This issue has been patched in versions 2.11.38 and 3.6.9. Traefik's management of TLS handshakes on TCP routers is vulnerable to a denial-of-service attack. An attacker can exploit this by sending an incomplete TLS record, causing the handshake to stall, and holding connections open. By opening many such stalled connections in parallel, an attacker can exhaust file descriptors and goroutines, degrading availability of all services on the affected entrypoint.

Vendor
traefik
Product
Unknown
CVSS
HIGH 7.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-03-05
Original CVE updated
2026-06-30
Advisory published
2026-03-05
Advisory updated
2026-06-30

Who should care

Users of Traefik, especially those who manage services behind Traefik, should be aware of this vulnerability. This includes administrators of web applications, cloud services, and any other infrastructure that relies on Traefik for routing and load balancing. Given the high severity of this vulnerability, immediate attention is required to ensure that Traefik is updated to a patched version.

Technical summary

The vulnerability in Traefik arises from its handling of TLS handshakes on TCP routers. When a TLS connection is processed, the read deadline used for protocol sniffing is cleared before the TLS handshake is completed. If a TLS handshake read error occurs, the code attempts a second handshake with different parameters, silently ignoring the initial error. An attacker can exploit this by sending an incomplete TLS record and stopping further data transmission. This causes the TLS handshake to stall indefinitely, holding connections open. By opening many such stalled connections, an attacker can exhaust system resources, leading to a denial of service.

Defensive priority

High. Immediate patching of Traefik to version 2.11.38 or 3.6.9 is recommended to prevent exploitation. Additionally, monitoring for unusual traffic patterns and connection attempts can help detect potential attacks.

Recommended defensive actions

  • Update Traefik to version 2.11.38 or 3.6.9 immediately.
  • Monitor for unusual traffic patterns and connection attempts.
  • Implement additional security measures such as rate limiting and IP blocking.
  • Review and update incident response plans to address potential denial-of-service attacks.
  • Consider implementing compensating controls such as Web Application Firewalls (WAFs).

Evidence notes

The CVE-2026-26999 vulnerability was publicly disclosed on March 5, 2026, and has been modified on June 30, 2026. The vulnerability affects Traefik versions prior to 2.11.38 and 3.6.9. The CVSS score for this vulnerability is 7.5, indicating a high severity. The vulnerability allows an attacker to cause a denial of service by sending an incomplete TLS record, which can stall the TLS handshake indefinitely.

Official resources

This article is AI-assisted and based on the supplied source corpus.