CVE-2026-6276: Haxx Curl

High severity, CVSS 7.5. EPSS: 0.3% chance of exploitation in the next 30 days.

Using libcurl, when a custom `Host:` header is first set for an HTTP request and a second request is subsequently done using the same *easy handle* but without the custom `Host:` header set, the second request would use stale information and pass on cookies meant for the first host in the second request. Leak them.

Affected products

• Haxx Curl: from 7.71.0, before 8.20.0 (fixed in 8.20.0)

Published 2026-05-13. Last modified 2026-09-15.