Canonical ubuntu-pro-client APT Source File Generation ubuntu-.list str.format directives.aptURL/suites[]/additionalPackages[] input validation

Summaryinfo

A vulnerability, which was classified as very critical, was found in Canonical ubuntu-pro-client. This vulnerability affects the function str.format of the file /etc/apt/sources.list.d/ubuntu-.list of the component APT Source File Generation. Such manipulation of the argument directives.aptURL/suites[]/additionalPackages[] leads to input validation. This vulnerability is traded as CVE-2026-11386. The attack may be launched remotely. There is no exploit available.

Detailsinfo

A vulnerability, which was classified as very critical, has been found in Canonical ubuntu-pro-client (affected version not known). Affected by this issue is the function str.format of the file /etc/apt/sources.list.d/ubuntu-.list of the component APT Source File Generation. The manipulation of the argument directives.aptURL/suites[]/additionalPackages[] with an unknown input leads to a input validation vulnerability. Using CWE to declare the problem leads to CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. Impacted is confidentiality, integrity, and availability. CVE summarizes:

An input validation and injection vulnerability exists in Canonical ubuntu-pro-client (formerly ubuntu-advantage-tools). The client constructs APT source files (such as /etc/apt/sources.list.d/ubuntu-.list or their DEB822 equivalents) using data received directly from the contract server response via the directives.suites[] and directives.aptURL fields. Because the client utilizes Python's str.format() to write these files without performing escaping, validation, or newline character filtering, a malicious or tampered contract response containing embedded newline (\n) characters can successfully inject arbitrary, attacker-controlled deb configuration lines into root-owned APT sources. When combined with the unvalidated additionalPackages[] field—which is passed positionally into a root-executed apt-get install command—an attacker capable of spoofing or manipulating the contract response (e.g., via a compromised internal infrastructure, an intercepted connection utilizing a trusted CA, or local logical bugs) can force the client to fetch and install malicious packages. This ultimately leads to arbitrary code execution with root privileges on the affected system. This component is preinstalled on supported Ubuntu Server releases and auto-attaches by default on cloud provider Ubuntu Pro images.

The advisory is available at ubuntu.com. This vulnerability is handled as CVE-2026-11386 since 06/05/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. Technical details are known, but there is no available exploit. The structure of the vulnerability defines a possible price range of USD $0-$5k at the moment (estimation calculated on 07/16/2026).

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-44911). If you want to get best quality of vulnerability data, you may have to visit VulDB.

Productinfo

Vendor

• Canonical

Name

• ubuntu-pro-client

License

• open-source

CPE 2.3info

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CPE 2.2info

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If you want to get best quality of vulnerability data, you may have to visit VulDB.

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