CVE-2026-12064

proto-default skips SSH verification

Published Jul 3, 2026 CVSS 3.1 · 7.5 High EPSS < 1% KEV · Not listed
Description
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Ubuntu USN Ubuntu USN USN-8525-1 curl vulnerabilities
History
Type Values Removed Values Added
Weaknesses CWE-297
Type Values Removed Values Added
Weaknesses CWE-760
Type Values Removed Values Added
Weaknesses CWE-760
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N'}

ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
Weaknesses CWE-287
Type Values Removed Values Added
Weaknesses CWE-287
Type Values Removed Values Added
Weaknesses CWE-287
Type Values Removed Values Added
Weaknesses CWE-287
Type Values Removed Values Added
Weaknesses CWE-287
Type Values Removed Values Added
Weaknesses CWE-287
Type Values Removed Values Added
First Time appeared Curl
Curl curl
Vendors & Products Curl
Curl curl
Type Values Removed Values Added
Description 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.
Title proto-default skips SSH verification
References
Weaknesses

Sources

Status
PUBLISHED
Assigner
curl
Published
Updated
Sep 15, 2026, 6:02 AM
Reserved
Jun 12, 2026, 7:23 AM
Status
Modified
Published
Jul 3, 2026, 7:16 AM
Modified
Sep 15, 2026, 7:16 AM
Severity
Important
Public date
Jul 3, 2026, 6:13 AM