cURL SSH Host Verification Bypass via Schemaless URL & --proto-default
CVE-2026-12064 Published on July 3, 2026

proto-default skips SSH verification
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.

NVD

Vulnerability Analysis

CVE-2026-12064 is exploitable with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. An automatable proof of concept (POC) exploit exists. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality, a high impact on integrity, and no impact on availability.

Attack Vector:
NETWORK
Attack Complexity:
LOW
Privileges Required:
NONE
User Interaction:
NONE
Scope:
UNCHANGED
Confidentiality Impact:
NONE
Integrity Impact:
HIGH
Availability Impact:
NONE

Weakness Type

Improper Validation of Certificate with Host Mismatch

The software communicates with a host that provides a certificate, but the software does not properly ensure that the certificate is actually associated with that host.


Products Associated with CVE-2026-12064

You can be notified by email with stack.watch whenever vulnerabilities like CVE-2026-12064 are published in these products:

Haxx Curl
 
Canonical Ubuntu Linux
 
Red Hat Http Server
 

Affected Versions

curl: curl: curl:

Exploit Probability

EPSS
0.40%
Percentile
31.55%

EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.