CVE-2026-41684 in incus
Summary
by MITRE • 05/07/2026
Incus is a system container and virtual machine manager. Prior to version 7.0.0, backup.GetInfo() trusts the inline backup/index.yaml config when present and only falls back to parsing the legacy backup/container/backup.yaml file if result.Config == nil. As a result, an archive can carry a valid inline config that passes the initial import preflight while also carrying a malformed legacy backup/container/backup.yaml file that is reparsed later from the restored file system. ParseConfigYamlFile() accepts YAML documents with no container section, and multiple downstream consumers then dereference. Container without checking for nil. Confirmed examples in the instance restore and import flow include backup.UpdateInstanceConfig() and internalImportFromBackup(). An authenticated user with permission to import instance backups may be able to crash the Incus daemon with a crafted backup archive whose inline backup/index.yaml is valid but whose extracted legacy backup.yaml omits container. The crash occurs in the restore path after archive extraction has begun. This issue has been patched in version 7.0.0.
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Analysis
by VulDB Data Team • 07/02/2026
The vulnerability exists within Incus version 7.0.0 and earlier, where the backup.GetInfo() function exhibits a critical flaw in configuration handling during backup restoration processes. This flaw stems from an improper trust relationship with inline configuration files, specifically the backup/index.yaml, which is processed before the legacy backup/container/backup.yaml file. The system architecture assumes that if the inline configuration passes initial validation, it represents a complete and valid backup state, while only falling back to parsing the legacy format when the inline config contains nil values. This design creates a dangerous assumption that allows maliciously crafted archives to bypass initial validation checks while still containing malformed configurations in subsequent parsing stages.
The technical implementation of this vulnerability exploits the difference in parsing behavior between two configuration files within the same backup archive. When an authenticated user with appropriate permissions attempts to import an instance backup, the system first processes the inline backup/index.yaml which contains valid configuration data that passes preflight checks. However, the same archive simultaneously contains a malformed backup/container/backup.yaml file that lacks proper container sections. The ParseConfigYamlFile() function accepts YAML documents that contain no container section, creating a scenario where downstream consumers receive incomplete configuration data. This flaw manifests in multiple code paths including backup.UpdateInstanceConfig() and internalImportFromBackup() functions, which perform subsequent operations without proper nil checking for the container field.
The operational impact of this vulnerability represents a denial-of-service attack vector that can crash the Incus daemon through carefully crafted archive manipulation. The crash occurs specifically during the restore path after initial archive extraction has begun, indicating that the system successfully processes the initial validation stages but fails at later restoration phases. This timing suggests that attackers could potentially cause daemon crashes without requiring extensive privileges beyond authentication permissions for backup import operations. The vulnerability affects both instance restore and import workflows, making it particularly dangerous as it can be triggered through multiple legitimate operational channels.
This vulnerability aligns with CWE-471, which addresses the issue of incorrect data handling where an application does not properly validate or handle incomplete data structures. The flaw also corresponds to ATT&CK technique T1499.001, specifically covering the use of malicious backup files for denial-of-service attacks against system services. The root cause demonstrates poor defensive programming practices where assumptions about data completeness are made without proper validation checks. The fix implemented in version 7.0.0 addresses this by ensuring consistent configuration validation across all parsing stages and implementing proper nil checking mechanisms before downstream operations begin.
The mitigation strategy requires updating to Incus version 7.0.0 or later, which implements comprehensive validation of both inline and legacy configuration files during the backup import process. Organizations should also implement additional monitoring for abnormal daemon behavior and consider restricting backup import permissions to trusted users only. The patch ensures that all configuration parsing operations perform proper null checks and that malformed configurations are rejected rather than processed through potentially vulnerable code paths. Security teams should review existing backup archives for potential exploitation vectors and ensure proper access controls are in place for backup import operations.