CVE-2026-9547: Haxx Curl

High severity, CVSS 7.4. EPSS: 0.3% chance of exploitation in the next 30 days.

When a libcurl-based application performs transfers via `SCP://` or `SFTP://` and utilizes the `CURLOPT_SSH_KEYFUNCTION` callback, it may silently accept an untrusted server. This vulnerability occurs when a server presents a host key type that does not match the specific key type already recorded for that host in the `known_hosts` file. Instead of rejecting the mismatch, the callback mechanism fails to properly enforce the restriction, allowing the connection to succeed without warning and risking a potential man-in-the-middle attack.

Affected products

• Haxx Curl: from 7.69.0, before 8.21.0 (fixed in 8.21.0)

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