CVE-2026-26999
Published: 05 March 2026
Summary
CVE-2026-26999 is a high-severity Uncontrolled Resource Consumption (CWE-400) vulnerability in Traefik Traefik. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Application or System Exploitation (T1499.004); ranked at the 5.7th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SC-5 (Denial-of-service Protection) and SC-6 (Resource Availability).
Deeper analysis
CVE-2026-26999 is a vulnerability in Traefik, an HTTP reverse proxy and load balancer, affecting versions prior to 2.11.38 and 3.6.9. It stems from improper management of TLS handshakes on TCP routers, where the read deadline used for protocol sniffing is cleared before the handshake completes. When a TLS handshake read error occurs, Traefik attempts a second handshake with altered connection parameters while silently ignoring the initial error, as rated at CVSS 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) and mapped to CWE-400 (Uncontrolled Resource Consumption).
A remote unauthenticated attacker can exploit this by sending an incomplete TLS record over a TCP router and halting further data transmission. This causes the TLS handshake to stall indefinitely, holding the connection open. By opening many such stalled connections in parallel, the attacker exhausts file descriptors and goroutines, degrading availability of all services on the affected Traefik entrypoint and resulting in a denial-of-service condition.
The vulnerability has been patched in Traefik versions 2.11.38 and 3.6.9. Mitigation involves upgrading to these fixed releases, with details available in the release notes at https://github.com/traefik/traefik/releases/tag/v2.11.38 and https://github.com/traefik/traefik/releases/tag/v3.6.9, as well as the security advisory at https://github.com/traefik/traefik/security/advisories/GHSA-xw98-5q62-jx94.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-9844
Vulnerability details
Traefik is an HTTP reverse proxy and load balancer. Prior to versions 2.11.38 and 3.6.9, there is a potential vulnerability in Traefik managing TLS handshake on TCP routers. When Traefik processes a TLS connection on a TCP router, the read…
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deadline used to bound protocol sniffing is cleared before the TLS handshake is completed. When a TLS handshake read error occurs, the code attempts a second handshake with different connection parameters, silently ignoring the initial error. A remote unauthenticated client can exploit this by sending an incomplete TLS record and stopping further data transmission, causing the TLS handshake to stall indefinitely 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. This issue has been patched in versions 2.11.38 and 3.6.9.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
The CVE describes remote exploitation of a TLS handshake resource exhaustion flaw in the public-facing Traefik proxy, directly enabling an application/system exploitation denial-of-service condition via stalled connections.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Flaw remediation directly addresses this CVE by requiring timely patching to Traefik versions 2.11.38 or 3.6.9, eliminating the improper TLS handshake management causing stalled connections.
Denial-of-service protection implements measures to limit effects of resource exhaustion attacks like parallel stalled TLS handshakes exhausting file descriptors and goroutines.
Resource availability establishes allocation limits and protections to prevent degradation from excessive open connections triggered by incomplete TLS records on TCP routers.