CVE-2026-11386: canonical ubuntu-pro-client (ubuntu-advantage-tools) Improper Input Validation

Vulnerability summary

CVE-2026-11386 is a critical (CVSS 9.0) Improper Input Validation vulnerability in canonical ubuntu-pro-client (ubuntu-advantage-tools). EPSS estimates a 0.53% chance of exploitation in the next 30 days, higher than 43.2% of scored vulnerabilities.

Timeline

1. 16-07-2026
   PublishedVulnerability first disclosed.
2. 16-07-2026
   Last modifiedVulnerability information updated.

Description

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.

• CWE-20Improper Input ValidationThe 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.