Critical Input validation

CVE-2026-11386 — ubuntu-pro-client Input Validation Vulnerability Leading to Arbitrary APT Directive Injection and Remote Code Execution

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.

Published Jul 16, 2026 · Updated Oct 15, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: canonical

Low

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.

How the score was calculated

Technical severity (critical)+10

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation

Not confirmed

Not in CISA KEV — an absence of record, not proof it is unexploited.

EPSS FIRST

—

No EPSS score.

Affects

Canonical

Ubuntu 14.04 LTS and 7 more

CVSS base

9.0

Critical · 2 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation

None

none · proof-of-concept · active

Automatable

can an attacker script the kill-chain steps

Technical impact

Total

partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (Canonical Ubuntu 14.04 LTS, Canonical Ubuntu 16.04 LTS, Canonical Ubuntu 18.04 LTS…).
The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
No fix documented in the sources: reduce exposure and monitor the vendor advisory.
Search available logs for exploit probes matching the vulnerability class (input validation), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
Canonical	Ubuntu 14.04 LTS	versions not specified by the source	Vulnerable	CVE Program (cve.org) e CISA ADP
Canonical	Ubuntu 16.04 LTS	versions not specified by the source	Vulnerable	CVE Program (cve.org) e CISA ADP
Canonical	Ubuntu 18.04 LTS	versions not specified by the source	Vulnerable	CVE Program (cve.org) e CISA ADP
Canonical	Ubuntu 20.04 LTS	versions not specified by the source	Vulnerable	CVE Program (cve.org) e CISA ADP
Canonical	Ubuntu 22.04 LTS	versions not specified by the source	Vulnerable	CVE Program (cve.org) e CISA ADP
Canonical	Ubuntu 24.04 LTS	versions not specified by the source	Vulnerable	CVE Program (cve.org) e CISA ADP
Canonical	Ubuntu 26.04 LTS	versions not specified by the source	Vulnerable	CVE Program (cve.org) e CISA ADP
Canonical	Ubuntu-pro-client (ubuntu-advantage-tools)	< 37.3	Vulnerable	CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector

Network

Attack complexity

High

Privileges required

None

User interaction

None

Scope

Changed

Confidentiality

High

Integrity

High

Availability

High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Scored by
9.0	CVSS 3.1	Critical	2.2	6.0	security@ubuntu.com via NIST National Vulnerability Database
9.0	CVSS 3.1	Critical	—	—	canonical via CVE Program (cve.org) e CISA ADP

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H (score shown at the top: security@ubuntu.com)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-20 · Improper Input Validation

Other CVEs with this weakness →

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).

web/proxy/WAF logsnetwork IDS/IPS

Timeline

What happened to this CVE, newest first.

2026
Affected products added · canonical/ubuntu-pro-client (ubuntu-advantage-tools), canonical/ubuntu 26.04 lts, canonical/ubuntu 24.04 lts, canonical/
Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
SSVC assessment updated
Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
Record published
Oct 15, 2026
CVSS changed · 9.0
Oct 15, 2026 · NIST National Vulnerability Database
Source status changed · → Awaiting Analysis
Oct 15, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 15, 2026 · NIST National Vulnerability Database
CVE published
Jul 16, 2026 · canonical

Source activity

Repeated readings are counted rather than listed.

1× Official description updated · Oct 15, 2026 – Oct 15, 2026

References

1 on the record

ubuntu.com/security/CVE-2026-11386
vdb-entry, NIST National Vulnerability Database

Elsewhere on this site

Canonical
every CVE for this vendor

Input validation
same class

CWE-20
other pages naming this weakness

Related CVEs (same products)

High CVE-2026-8933 snap-confine Local Privilege Escalation via Capabilities Misconfiguration or Flaw in Execution Environment Setup Jul 21, 2026
High CVE-2026-15226 snapd snap-confine Sandbox Confinement Bypass via Omission of setuid Restriction in Seccomp Templates Jul 21, 2026
Medium CVE-2024-5300 AppArmor Base Profile Misconfiguration in snapd Permits Confined Snaps Unauthorized Access to Hashed Passwords via systemd-userdbd Jul 21, 2026
Medium CVE-2026-9494 ubuntu-pro-client Information Disclosure via Cleartext Bearer Token Exposure in Process Command Line Jul 16, 2026
Medium CVE-2026-12391 ubuntu-pro-client Local Privilege Escalation and Information Disclosure via Symlink Arbitrary File Read in collect-logs Jul 16, 2026
Critical CVE-2026-12249 Canonical ADSys plaintext HTTP CA certificate retrieval enables trust store poisoning Jun 22, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No FIRST EPSS score.
No fixed version, patch or mitigation documented.
No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-11386 is "ubuntu-pro-client Input Validation Vulnerability Leading to Arbitrary APT Directive Injection and Remote Code Execution", rated Critical. It affects Ubuntu 14.04 LTS (Canonical); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 9.0 describes technical severity. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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