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.
Weakness
The product communicates with a host that provides a certificate, but the product does not properly ensure that the certificate is actually associated with that host.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Curl | Haxx | 7.81.0 (including) | 8.21.0 (excluding) |
| Red Hat Enterprise Linux 10 | RedHat | curl-0:8.12.1-4.el10_2.3 | * |
| Red Hat Enterprise Linux 10.0 Extended Update Support | RedHat | curl-0:8.12.1-1.el10_0.10 | * |
| Red Hat Hardened Images | RedHat | curl-main-8.21.0-0.1.hum1 | * |
| Red Hat Hardened Images | RedHat | rust-main-1.96.1-1.hum1 | * |
| Curl | Ubuntu | devel | * |
| Curl | Ubuntu | questing | * |
| Curl | Ubuntu | resolute | * |
| Curl | Ubuntu | upstream | * |
Extended Description
Even if a certificate is well-formed, signed, and follows the chain of trust, it may simply be a valid certificate for a different site than the site that the product is interacting with. In order to ensure data integrity, the certificate must be valid, and it must pertain to the site that is being accessed. Even if the product attempts to check the hostname, it is still possible to incorrectly check the hostname. For example, attackers could create a certificate with a name that begins with a trusted name followed by a NUL byte, which could cause some string-based comparisons to only examine the portion that contains the trusted name.