CVE-2026-11586: Haxx Curl

High severity, CVSS 7.5. EPSS: 0.6% chance of exploitation in the next 30 days.

By default, curl automatically responds to WebSocket PING frames. Because curl lacks an upper bound on memory allocation for unacknowledged frames, a malicious server can exhaust all available memory by flooding curl with rapid, sequential PING messages.

Affected products

• Haxx Curl: from 8.16.0, before 8.21.0 (fixed in 8.21.0)

Published 2026-07-03. Last modified 2026-09-15.