High [CVE-2026-12064] SSH host verification bypass when using schemeless URLs with SFTP/SCP
This high-severity Red Hat Linux advisory covers CVE-2026-12064 affecting Red Hat Enterprise Linux 10, Red Hat Hardened Images, Red Hat package: curl.
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Summary
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. 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.
Red Hat severity: Important — CVSS 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N). Weakness: CWE-358.
Affected Red Hat products: Red Hat Enterprise Linux 10; Red Hat Hardened Images.
Affected products named by the advisory: Red Hat package: curl.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · high-confidence parse· fetched 12 days ago·verify at source
- curl-0:8.12.1-4.el10_2.3
- curl-main-8.21.0-0.1.hum1
- rust-main-1.96.1-1.hum1
- RHSA-2026:55450
- RHSA-2026:29017
- RHSA-2026:34975
Official advisory · high-confidence parse· fetched 12 days ago·verify at source
Mitigation checklist
- To mitigate this issue, avoid using the `--proto-default sftp` or `--proto-default scp` options with schemeless URLs when invoking the `curl` command. Instead, explicitly specify the protocol in the URL (e.g., `sftp://host/path` or `scp://host/path`).
Official advisory · high-confidence parse· fetched 12 days ago·verify at source
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