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.

suse_linux SUSE-SU-2026:2925-1: SUSE SLED15 / SLES15 : Security update for curl (Important) (SUSE-SU-2026:2925-1)

suse_linux SUSE-SU-2026:2926-1: SUSE SLES15 : Security update for curl (Important) (SUSE-SU-2026:2926-1)

The remote openSUSE 16 host has packages installed that are affected by multiple vulnerabilities as referenced in the openSUSE-SU-2026:21272-1 advisory.

    This update for curl fixes the following issues

    - CVE-2026-8286: wrong STARTTLS connection reuse (bsc#1268402).
    - CVE-2026-8458: wrong reuse for different services (bsc#1268407).
    - CVE-2026-8924: traling dot domain super cookie (bsc#1268409).
    - CVE-2026-8927: env-set cross-proxy Digest auth state leak (bsc#1268413).
    - CVE-2026-9079: stale proxy password leak (bsc#1268415).
    - CVE-2026-9080: UAF after pause in socket callback (bsc#1268416).
    - CVE-2026-9545: exposing HTTP/3 early data (bsc#1268417).
    - CVE-2026-9547: SSH improper host validation (bsc#1268420).
    - CVE-2026-10536: HTTP/2 stream-dependency tree UAF (bsc#1268422).
    - CVE-2026-12064: proto-default skips SSH verification (bsc#1268427).

Tenable has extracted the preceding description block directly from the SUSE security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The remote Ubuntu 14.04 LTS / 16.04 LTS / 18.04 LTS / 20.04 LTS / 24.04 LTS / 26.04 LTS host has packages installed that are affected by multiple vulnerabilities as referenced in the USN-8525-1 advisory.

    Harry Sintonen discovered that curl incorrectly handled credentials when following HTTP redirects in     conjunction with .netrc files. An attacker could possibly use this issue to obtain sensitive information.
    This issue only affected Ubuntu 14.04 LTS, Ubuntu 16.04 LTS, and Ubuntu 18.04 LTS. (CVE-2024-11053)

    Hiroki Kurosawa discovered that curl incorrectly handled OCSP stapling responses. A remote attacker could     possibly use this issue to obtain sensitive information. This issue only affected Ubuntu 16.04 LTS and     Ubuntu 18.04 LTS. (CVE-2024-8096)

    Joshua Rogers discovered that curl had a use-after-free vulnerability when resetting and cleaning up     HTTP/2 stream handles. An attacker could possibly use this issue to cause a denial of service or execute     arbitrary code. This issue only affected Ubuntu 24.04 LTS, Ubuntu 25.04, and Ubuntu 25.10.
    (CVE-2026-10536)

    Quac Tran and Ngoc Hieu discovered that curl incorrectly reused connections when switching authentication     methods to the same host. An attacker could possibly use this issue to obtain sensitive information or     perform unauthorized actions. This issue only affected Ubuntu 20.04 LTS. (CVE-2026-5545)

    Osama Hamad discovered that curl incorrectly reused SMB connections when the target share differed between     transfers. An attacker could possibly use this issue to obtain sensitive information. This issue only     affected Ubuntu 16.04 LTS, Ubuntu 18.04 LTS, and Ubuntu 20.04 LTS. (CVE-2026-5773)

    Muhamad Arga Reksapati discovered that curl incorrectly forwarded Digest proxy authentication credentials     to a different proxy host. An attacker could possibly use this issue to obtain sensitive information. This     issue only affected Ubuntu 18.04 LTS and Ubuntu 20.04 LTS. (CVE-2026-7168)

    It was discovered that curl incorrectly skipped SSH host verification options when using schemeless URLs     with --proto-default. An attacker could possibly use this issue to perform machine-in-the-middle attacks.
    This issue only affected Ubuntu 25.04 and Ubuntu 25.10. (CVE-2026-12064)

    It was discovered that curl did not enforce an upper bound on memory allocated for unacknowledged     WebSocket PING frames. A remote attacker could possibly use this issue to cause a denial of service. This     issue only affected Ubuntu 25.10. (CVE-2026-11586)

    It was discovered that curl could stall indefinitely when a malicious HTTP/3 server sent a continuous     stream of empty UDP datagrams. A remote attacker could possibly use this issue to cause a denial of     service. This issue only affected Ubuntu 25.10. (CVE-2026-11352)

    It was discovered that curl could incorrectly continue trusting a native platform CA store after an     application switched the handle to use custom CA material. An attacker could possibly use this issue to     obtain sensitive information. This issue only affected Ubuntu 25.10. (CVE-2026-11564)

Tenable has extracted the preceding description block directly from the Ubuntu security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The version of curl installed on the remote host is 7.81.0 prior to 8.21.0. It is, therefore, affected by an improper host validation vulnerability:

  - When a user invokes curl using a schemeless URL combined with --proto-default sftp, a disconnect occurs     that erroneously bypasses the initialization of critical SSH security options. (CVE-2026-12064)

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - 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.
    (CVE-2026-12064)

Note that Nessus relies on the presence of the package as reported by the vendor.

ID	Name	Product	Family	Severity
326418	openSUSE 16: curl / curl-fish-completion / curl-zsh-completion / libcurl-devel / etc (openSUSE-SU-2026:21272-1)	Nessus	SuSE Local Security Checks	critical
326253	Ubuntu 14.04 LTS / 16.04 LTS / 18.04 LTS / 20.04 LTS / 24.04 LTS / 26.04 LTS : curl vulnerabilities (USN-8525-1)	Nessus	Ubuntu Local Security Checks	high
323014	Curl 7.81.0 < 8.21.0 Proto-Default Skips SSH Verification	Nessus	Misc.	high
322467	Linux Distros Unpatched Vulnerability : CVE-2026-12064	Nessus	Misc.	high

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