[Ovmsdev] Registered phone / password security issue

Mark Webb-Johnson mark at webb-johnson.net
Wed Jul 22 10:02:05 HKT 2015

Michael, Tom,

Not sure how the entire EEPROM can be erased. The code in par_write(), par_set() and par_setbin() seems to limit the write to PARAM_MAX_LENGTH. The EEPROM can’t be overwritten by normal code and it takes quite a bit of register mashing to write to it. Can someone have a look over the params.c functions and see if you have any guesses as to the cause? I think it is important to identify the root cause.

I did fix an error in the acc code, December last year, that caused an off-by-one parameter to be set:

commit 5269c870b1858f58098b16b39d10beb2b0e3b330
Author: Mark Webb-Johnson <mark at webb-johnson.net>
Date:   Mon Dec 8 13:11:32 2014 +0800

    Setting acc params, without location, when not in a location, leads to off-by-one index parameter write

diff --git a/vehicle/OVMS.X/acc.c b/vehicle/OVMS.X/acc.c
index 4935590..1bf430c 100644
--- a/vehicle/OVMS.X/acc.c
+++ b/vehicle/OVMS.X/acc.c
@@ -948,7 +948,7 @@ BOOL acc_cmd_params(BOOL sms, char* caller, char *arguments)

-  if (k<0)
+  if (k<=0)
     s = stp_rom(net_scratchpad,ACC_NOTHERE);

That is in the development branch, but is not in the standard firmware. But, the worst affect of that would be to overwrite PARAM_COOLDOWN (#15) (and easy to see as the overwritten value is base64).

It seems to be that params.c sets the default values to be:


My only concern with removing the fail-open to both PARAM_REGPHONE (net_sms_checkcaller) and PARAM_MODULEPASS (net_sms_checkpassarg) is that if they were both blank then the user would be completely locked out of the module. Only solution would be a complete re-flash and reset to default parameters.

Another option would be to hard-code change par_write() to refuse to write a blank password to #1. Then, we could go ahead and change net_sms_checkcaller() to not fail open for registered phone number. From what I can see, all writes to EEPROM go through par_write() in params.c.

Regards, Mark.

> On 22 Jul, 2015, at 8:39 am, Tom Saxton <tom at idleloop.com> wrote:
> Hi Michael,
> Have you confirmed the security problem? I've had time when the EEPROM got
> zeroed out and I couldn't access the module via SMS at all. I had to
> reflash with a valid EEPROM image in order to re-register my cell number.
> I'm pretty careful not to share my OVMS phone number with anyone. If
> someone unfriendly had it, they could send it a bunch of SMS messages each
> of which costs me a penny. Do that 1,000 times, and they've disabled my
> box until I refill my H2O account.
>   Tom
> -----Original Message-----
> From: Michael Balzer <dexter at expeedo.de>
> Reply-To: OVMS Developers <ovmsdev at lists.teslaclub.hk>
> Date: Tuesday, July 21, 2015 at 9:23 AM
> To: OVMS Developers <ovmsdev at lists.teslaclub.hk>
> Subject: [Ovmsdev] Registered phone / password security issue
>> Hi everyone,
>> some users including me experienced loss or garbling of eeprom
>> parameters. I once saw by chance that my registered phone number had
>> turned empty -- I seldom need to use SMS, so I only saw this when
>> checking the parameter list on the App for another config.
>> The same now also occured to another user I'm in contact with, and it
>> now turned out that's not only annoying but a security issue:
>> The current logic of net_sms_checkcaller() allows access to any phone
>> number if the parameter is empty. The same applies to
>> net_sms_checkpassarg(), which will allow any password to be used if no
>> password is stored.
>> As this kind of data loss can only be detected by checking the
>> parameters, it's possible to check for "open" modules by just trying to
>> access them from time to time -- you only need to know the SIM card
>> number.
>> I'm about to submit a change for both functions to NOT allow access if
>> their respective param slots are empty.
>> As the initial flash contents has the "OVMS" standard password, a
>> completely lost module should still be restorable by re-flashing.
>> Do I miss something? Is there any reason for the "empty=wildcard"
>> behaviour?
>> Regards,
>> Michael
>> -- 
>> Michael Balzer * Helkenberger Weg 9 * D-58256 Ennepetal
>> Fon 02333 / 833 5735 * Handy 0176 / 206 989 26
>> _______________________________________________
>> OvmsDev mailing list
>> OvmsDev at lists.teslaclub.hk
>> http://lists.teslaclub.hk/mailman/listinfo/ovmsdev
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