How do I prevent permission escalation in Django admin when granting "user change" permission?

they gain the ability to set the is_superuser flag on any account, including their own. (!!!)

Not only this, they also gain the ability to give themselves any permissions one-by-one, same effect...

I'm sure it involves subclassing django.contrib.auth.forms.UserChangeForm

Well, not necessarily. The form you see in the change page of django's admin is dynamically created by the admin application, and based on UserChangeForm, but this class barely adds regex validation to the username field.

and hooking it into my already-custom UserAdmin object...

A custom UserAdmin is the way to go here. Basically, you want to change the fieldsets property to something like that :

class MyUserAdmin(UserAdmin):    fieldsets = (        (None, {'fields': ('username', 'password')}),        (_('Personal info'), {'fields': ('first_name', 'last_name', 'email')}),        # Removing the permission part        # (_('Permissions'), {'fields': ('is_staff', 'is_active', 'is_superuser', 'user_permissions')}),        (_('Important dates'), {'fields': ('last_login', 'date_joined')}),        # Keeping the group parts? Ok, but they shouldn't be able to define        # their own groups, up to you...        (_('Groups'), {'fields': ('groups',)}),    )

But the problem here is that this restriction will apply to all users. If this is not what you want, you could for example override change_view to behave differently depending on the permission of the users. Code snippet :

class MyUserAdmin(UserAdmin):    staff_fieldsets = (        (None, {'fields': ('username', 'password')}),        (_('Personal info'), {'fields': ('first_name', 'last_name', 'email')}),        # No permissions        (_('Important dates'), {'fields': ('last_login', 'date_joined')}),        (_('Groups'), {'fields': ('groups',)}),    )    def change_view(self, request, *args, **kwargs):        # for non-superuser        if not request.user.is_superuser:            try:                self.fieldsets = self.staff_fieldsets                response = super(MyUserAdmin, self).change_view(request, *args, **kwargs)            finally:                # Reset fieldsets to its original value                self.fieldsets = UserAdmin.fieldsets            return response        else:            return super(MyUserAdmin, self).change_view(request, *args, **kwargs)

The below part of the accepted answer has a race condition where if two staff users try to access the admin form at the same time, one of them may get the superuser form.

try:    self.readonly_fields = self.staff_self_readonly_fields    response = super(MyUserAdmin, self).change_view(request, object_id, form_url, extra_context, *args, **kwargs)finally:    # Reset fieldsets to its original value    self.fieldsets = UserAdmin.fieldsets

To avoid this race condition (and in my opinion improve the overall quality of the solution), we can override the get_fieldsets() and get_readonly_fields() methods directly:

class UserAdmin(BaseUserAdmin):    staff_fieldsets = (        (None, {'fields': ('username')}),        ('Personal info', {'fields': ('first_name', 'last_name', 'email')}),        # No permissions        ('Important dates', {'fields': ('last_login', 'date_joined')}),    )    staff_readonly_fields = ('username', 'first_name', 'last_name', 'email', 'last_login', 'date_joined')    def get_fieldsets(self, request, obj=None):        if not request.user.is_superuser:            return self.staff_fieldsets        else:            return super(UserAdmin, self).get_fieldsets(request, obj)    def get_readonly_fields(self, request, obj=None):        if not request.user.is_superuser:            return self.staff_readonly_fields        else:            return super(UserAdmin, self).get_readonly_fields(request, obj)

Great thanks to Clément. What I came up with when doing the same for my site is that I needed additionally to make all fields readonly for users you other than self. So basing on Clément's answer I addeed readonly fields and password field hiding when viewing not self

class MyUserAdmin(UserAdmin):    model = User    staff_self_fieldsets = (        (None, {'fields': ('username', 'password')}),        (_('Personal info'), {'fields': ('first_name', 'last_name', 'email')}),        # No permissions        (_('Important dates'), {'fields': ('last_login', 'date_joined')}),    )    staff_other_fieldsets = (        (None, {'fields': ('username', )}),        (_('Personal info'), {'fields': ('first_name', 'last_name', 'email')}),        # No permissions        (_('Important dates'), {'fields': ('last_login', 'date_joined')}),    )    staff_self_readonly_fields = ('last_login', 'date_joined')    def change_view(self, request, object_id, form_url='', extra_context=None, *args, **kwargs):        # for non-superuser        if not request.user.is_superuser:            try:                if int(object_id) != request.user.id:                    self.readonly_fields = User._meta.get_all_field_names()                    self.fieldsets = self.staff_other_fieldsets                else:                    self.readonly_fields = self.staff_self_readonly_fields                    self.fieldsets = self.staff_self_fieldsets                response = super(MyUserAdmin, self).change_view(request, object_id, form_url, extra_context, *args, **kwargs)            except:                logger.error('Admin change view error. Returned all readonly fields')                self.fieldsets = self.staff_other_fieldsets                self.readonly_fields = ('first_name', 'last_name', 'email', 'username', 'password', 'last_login', 'date_joined')                response = super(MyUserAdmin, self).change_view(request, object_id, form_url, extra_context, *args, **kwargs)            finally:                # Reset fieldsets to its original value                self.fieldsets = UserAdmin.fieldsets                self.readonly_fields = UserAdmin.readonly_fields            return response        else:            return super(MyUserAdmin, self).change_view(request, object_id, form_url, extra_context, *args, **kwargs)