CVE-2026-34178

CriticalPublic PoC

Published: 09 April 2026

Published

09 April 2026

Modified

22 April 2026

KEV Added

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Patch

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CVSS Score 9.1 CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H

EPSS Score 0.0005 14.8th percentile

Risk Priority 18 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2026-34178 is a critical-severity Improper Input Validation (CWE-20) vulnerability in Canonical Lxd. Its CVSS base score is 9.1 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 14.8th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified are NIST 800-53 SI-10 (Information Input Validation) and SI-2 (Flaw Remediation).

Threat & Defense at a Glance

What attackers do: exploitation maps to Exploitation for Privilege Escalation (T1068) and 1 other technique. What defenders deploy: see the NIST 800-53 controls recommended below.

Threat & Defense Details

Mitigating Controls (NIST 800-53 r5)AI

SI-10 Information Input Validation good match

prevent

Directly addresses the improper input validation vulnerability by requiring checks on all relevant files, including backup/container/backup.yaml, against project restrictions during tar archive import.

SI-2 Flaw Remediation good match

prevent

Ensures timely identification, reporting, and patching of the specific flaw in LXD backup import functionality to prevent exploitation.

AC-6 Least Privilege partial match

prevent

Enforces least privilege by restricting instance-creation permissions to only necessary users, reducing the population able to craft and import malicious backup archives.

MITRE ATT&CK Enterprise TechniquesAI

T1068 Exploitation for Privilege Escalation Privilege Escalation

Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.

attack.mitre.org →

T1611 Escape to Host Privilege Escalation

Adversaries may break out of a container or virtualized environment to gain access to the underlying host.

attack.mitre.org →

Why these techniques?

Improper input validation bypasses LXD project restrictions to create privileged containers, directly enabling privilege escalation (T1068) and facilitating container escape to host for full compromise (T1611).

Confidence: HIGH · MITRE ATT&CK Enterprise v18.1

NVD Description

In Canonical LXD before 6.8, the backup import path validates project restrictions against backup/index.yaml in the supplied tar archive but creates the instance from backup/container/backup.yaml, a separate file in the same archive that is never checked against project restrictions. An…

authenticated remote attacker with instance-creation permission in a restricted project can craft a backup archive where backup.yaml carries restricted settings such as security.privileged=true or raw.lxc directives, bypassing all project restriction enforcement and allowing full host compromise.

Deeper analysisAI

CVE-2026-34178 is an improper input validation vulnerability (CWE-20) in Canonical LXD versions prior to 6.8. The issue lies in the backup import functionality, where project restrictions are enforced by validating the backup/index.yaml file within a supplied tar archive. However, the instance is actually created using the separate backup/container/backup.yaml file, which is not checked against project restrictions. This discrepancy allows attackers to embed unauthorized configurations in the unchecked file. The vulnerability carries a CVSS v3.1 base score of 9.1 (AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H), indicating critical severity due to its potential for high-impact exploitation.

An authenticated remote attacker with instance-creation permissions in a restricted LXD project can exploit this by crafting a malicious tar archive backup. By placing restricted settings, such as security.privileged=true or raw.lxc directives, into the backup.yaml file while ensuring index.yaml passes validation, the attacker bypasses all project restrictions during import. Successful exploitation enables creation of a privileged container, leading to full host compromise through container escape and arbitrary code execution on the underlying system.

Mitigation is addressed in the referenced GitHub security advisory (GHSA-q96j-3fmm-7fv4) and pull request #17921, which patch the validation logic in LXD 6.8 and later versions. Security practitioners should upgrade to LXD 6.8 or higher and review access controls for instance-creation permissions in restricted projects to prevent exploitation.