CVE-2026-11352: Haxx Curl

High severity, CVSS 7.5. EPSS: 0.7% chance of exploitation in the next 30 days.

An issue in curl’s QUIC UDP receive function allows a malicious HTTP/3 server to trigger a remote denial of service against a curl or libcurl client. Because the helper function discards zero-length UDP datagrams before counting them toward the per-call packet budget, a connected QUIC peer can continuously stream empty datagrams to indefinitely stall the client.

Affected products

• Haxx Curl: from 8.18.0, before 8.21.0 (fixed in 8.21.0)

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