CVE-2026-41684

Details

It was found that 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.

The flow is as follows:
A crafted backup archive contains a valid backup/index.yaml file together with a malformed backup/container/backup.yaml file that omits the container section.
backup.GetInfo() parses backup/index.yaml successfully, so bInfo.Config is populated from the inline config.
Because result.Config != nil, GetInfo() does not fall back to backup/container/backup.yaml.
instances_post.go then builds the request from bInfo.Config.Container, which succeeds because the inline config is valid.
Later, storage unpack extracts backup/container/backup.yaml into the instance volume as /backup.yaml.
backend.go then calls backup.UpdateInstanceConfig(..., mountPath), which reparses /backup.yaml through ParseConfigYamlFile().
Because ParseConfigYamlFile() accepts YAML with no container section, backup.Container == nil, and later access to backup.Container.Devices or backup.Container.ExpandedDevices can trigger a nil-pointer dereference.

Affected Files:

• https://github.com/lxc/incus/blob/v6.22.0/internal/server/backup/backup_info.go#L87
• https://github.com/lxc/incus/blob/v6.22.0/internal/server/backup/backup_info.go#L115
• https://github.com/lxc/incus/blob/v6.22.0/internal/server/backup/backup_config_utils.go#L85
• https://github.com/lxc/incus/blob/v6.22.0/internal/server/backup/backup_config_utils.go#L159
• https://github.com/lxc/incus/blob/v6.22.0/internal/server/storage/backend.go#L809
• https://github.com/lxc/incus/blob/v6.22.0/cmd/incusd/api_internal.go#L749

The initial backup-metadata parser prefers inline backup/index.yaml content:

Affected Code:

if hdr.Name == backupIndexPath {
    err = yaml.NewDecoder(tr).Decode(&result)

The legacy backup/container/backup.yaml file is only parsed if the inline config is absent:

Affected Code:

if result.Config == nil && hdr.Name == "backup/container/backup.yaml" {
    err = yaml.NewDecoder(tr).Decode(&result.Config)

ParseConfigYamlFile() accepts an empty YAML document, or one with no container section, without validation:

Affected Code:

func ParseConfigYamlFile(path string) (*config.Config, error) {
    data, err := os.ReadFile(path)
    ...
    backupConf := config.Config{}
    err = yaml.Unmarshal(data, &backupConf)

UpdateInstanceConfig() conditionally uses backup.Container at first but later dereferences it unconditionally:

Affected Code:

if backup.Container != nil {
    backup.Container.Name = b.Name
    backup.Container.Project = b.Project
}

if updateRootDevicePool(backup.Container.Devices, pool.Name) {
    rootDiskDeviceFound = true
}

if updateRootDevicePool(backup.Container.ExpandedDevices, pool.Name) {
    rootDiskDeviceFound = true
}

Another confirmed sink is present in internalImportFromBackup():

Affected Code:

if allowNameOverride {
    backupConf.Container.Name = instName
}

if instName != backupConf.Container.Name {
    return fmt.Errorf("Instance name requested %q doesn't match instance name in backup config %q", instName, backupConf.Container.Name)
}

This was confirmed as follows:

Command:

go test ./test/fuzz -run='TestExtractedBackupYAMLMissingContainerNilDereference' -count=1 -v

Output:

=== RUN   TestExtractedBackupYAMLMissingContainerNilDereference
=== RUN   TestExtractedBackupYAMLMissingContainerNilDereference/legacy_backup_empty
   extracted_backup_yaml_poc_test.go:70: UpdateInstanceConfig panicked on malformed extracted
       backup.yaml (container is nil): runtime error: invalid memory address or nil pointer
       dereference
=== RUN   TestExtractedBackupYAMLMissingContainerNilDereference/legacy_backup_pool_only
   extracted_backup_yaml_poc_test.go:70: UpdateInstanceConfig panicked on malformed extracted
       backup.yaml (container is nil): runtime error: invalid memory address or nil pointer
       dereference
=== RUN   TestExtractedBackupYAMLMissingContainerNilDereference/legacy_backup_volume_only
   extracted_backup_yaml_poc_test.go:70: UpdateInstanceConfig panicked on malformed extracted
       backup.yaml (container is nil): runtime error: invalid memory address or nil pointer
       dereference
--- FAIL: TestExtractedBackupYAMLMissingContainerNilDereference (0.21s)
FAIL

It is recommended to validate the parsed legacy backup.yaml structure before any dereference and to fail with a standard error if Container is missing:

Proposed Fix:

if backup.Container == nil {
    return errors.New("No container struct in the backup file found")
}

That validation should be added at minimum in: backup.UpdateInstanceConfig() and internalImportFromBackup() before any backupConf.Container.* access

More broadly, it is recommended to centralize backup-config validation so that both inline backup/index.yaml and extracted legacy backup.yaml files are checked against the same structural requirements before any restore or import consumer uses them.

A patch is available at https://github.com/lxc/incus/releases/tag/v7.0.0.

Credit

This issue was discovered and reported by the team at 7asecurity (https://7asecurity.com/)

The application dereferences a null pointer, causing a crash. Typical impact: denial of service via crash.

CVE-2026-41684 has a CVSS score of 6.5 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. No fixed version is listed yet, so configuration controls and monitoring matter more in the interim.

Kodem intelligence

1. What is CVE-2026-41684? CVE-2026-41684 is a medium-severity null pointer dereference vulnerability in github.com/lxc/incus/v6/cmd/incusd (go), affecting versions <= 6.23.0. No fixed version is listed yet. The application dereferences a null pointer, causing a crash.
2. How severe is CVE-2026-41684? CVE-2026-41684 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/lxc/incus/v6/cmd/incusd are affected by CVE-2026-41684? github.com/lxc/incus/v6/cmd/incusd (go) versions <= 6.23.0 is affected.
4. Is there a fix for CVE-2026-41684? No fixed version is listed for CVE-2026-41684 yet. Monitor the advisory for updates and apply mitigations in the interim.
5. Is CVE-2026-41684 exploitable, and should I be worried? Whether CVE-2026-41684 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-41684 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-41684? No fixed version is listed yet. In the interim: Keep the dependency up to date. Ensure all pointers and return values are checked for null before use.

Other vulnerabilities in github.com/lxc/incus/v6/cmd/incusd