HAProxy 3 before 3.4.6 allows a remote unauthenticated attacker to cause a denial of service (persistent worker-thread CPU exhaustion) via an HTTP/1.1 chunked request

Overview

HAProxy 3 before 3.4.6 allows a remote unauthenticated attacker to cause a denial of service (persistent worker-thread CPU exhaustion) via an HTTP/1.1 chunked request. Although the H1 multiplexer drains the request before closing the stream, the parser repeatedly re-processes the same bytes without making progress. The affected thread stays busy at 100% CPU after timeouts expire and after the client disconnects, and repeated requests can consume all worker threads until the process is restarted.

Affected

• HAProxy >= 3.0.0 < 3.0.30
• HAProxy >= 3.2.0 < 3.2.26
• HAProxy >= 3.3.0 < 3.3.17
• HAProxy >= 3.4.0 < 3.4.6
• HAProxy >= 3.5-dev < 3.5-dev9
• enterprise_edition >= 3.0r1 < 3.0r1-362.1441
• enterprise_edition >= 3.2r1 < 3.2r1-378.1259
• enterprise_edition >= 3.3r1 < 3.3r1-377.1005
• haproxy_kubernetes_ingress_controller >= 3.2.0 < 3.2.17
• kubernetes_ingress_controller_enterprise >= 3.2.0 < 3.2.17-ee1
• kubernetes_ingress_controller_enterprise >= 3.0 < 3.0.16-ee17
• kubernetes_ingress_controller_enterprise >= 1.11 < 1.11.14-ee11

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.