Copyright © 2012 Red Hat, Inc. All rights reserved. Important 2026-07-03T06:13:55 curl: curl: SSH host verification bypass when using schemeless URLs with SFTP/SCP 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N CWE-358

When a user invokes curl using a schemeless URL combined with `--proto-default` sftp (or scp), a disconnect occurs between the tool layer and libcurl. The tool layer incorrectly infers the URL scheme, which erroneously bypasses the initialization of critical SSH security options like CURLOPT_SSH_HOST_PUBLIC_KEY_SHA256 and CURLOPT_SSH_KNOWNHOSTS. Conversely, the libcurl runtime successfully honors CURLOPT_DEFAULT_PROTOCOL and establishes the connection via SFTP/SCP as specified. Because the tool layer skipped the security configuration, these SSH host verification options are silently omitted, causing curl to connect to an unverified SSH remote host without throwing an error.

A flaw was found in curl. When a user invokes curl with a schemeless URL and specifies SFTP (SSH File Transfer Protocol) or SCP (Secure Copy Protocol) as the default protocol, the tool layer fails to initialize critical SSH security options. This bypasses host verification, allowing curl to connect to an unverified SSH remote host without alerting the user. This could enable an attacker to intercept or manipulate data through a man-in-the-middle attack.

This Important flaw in curl allows an attacker to bypass SSH host verification when a user invokes curl with a schemeless URL and specifies SFTP or SCP as the default protocol. This can lead to man-in-the-middle attacks, enabling data interception or manipulation without user awareness in Red Hat environments. Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability. Red Hat Hardened Images 2026-06-24T00:00:00Z RHSA-2026:29017 curl-main-8.21.0-0.1.hum1 Red Hat Hardened Images 2026-07-02T00:00:00Z RHSA-2026:34975 rust-main-1.96.1-1.hum1 Red Hat Enterprise Linux 10 Affected curl Red Hat Enterprise Linux 6 Affected curl Red Hat Enterprise Linux 7 Affected curl Red Hat Enterprise Linux 8 Affected curl Red Hat Enterprise Linux 9 Affected curl Red Hat OpenShift Container Platform 4 Affected rhcos Red Hat OpenShift Dev Spaces Affected devspaces/code-rhel9 Red Hat Trusted Profile Analyzer Affected rhtpa/rhtpa-trustification-service-rhel9 https://www.cve.org/CVERecord?id=CVE-2026-12064 https://nvd.nist.gov/vuln/detail/CVE-2026-12064 https://curl.se/docs/CVE-2026-12064.html https://curl.se/docs/CVE-2026-12064.json https://hackerone.com/reports/3797526