From debbugs-submit-bounces@debbugs.gnu.org Tue Apr 06 05:56:49 2021 Received: (at 47584) by debbugs.gnu.org; 6 Apr 2021 09:56:49 +0000 Received: from localhost ([127.0.0.1]:39234 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1lTiS1-0003fj-9B for submit@debbugs.gnu.org; Tue, 06 Apr 2021 05:56:49 -0400 Received: from albert.telenet-ops.be ([195.130.137.90]:40674) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1lTiRz-0003fZ-AE for 47584@debbugs.gnu.org; Tue, 06 Apr 2021 05:56:48 -0400 Received: from butterfly.local ([213.119.235.56]) by albert.telenet-ops.be with bizsmtp id pMwk240041Dh5Ut06MwlpH; Tue, 06 Apr 2021 11:56:45 +0200 Message-ID: <00621260aa43f1918aaf0f0bb2318bf359b826c3.camel@telenet.be> Subject: Re: bug#47584: Race condition in =?UTF-8?Q?=E2=80=98copy-account-skeletons=E2=80=99=3A?= possible privilege escalation. From: Maxime Devos To: Ludovic =?ISO-8859-1?Q?Court=E8s?= Date: Tue, 06 Apr 2021 11:56:23 +0200 In-Reply-To: <87zgycqzfz.fsf@gnu.org> References: <1a6ed722dfdd96dc8d53f939aa8e440ca7c29213.camel@telenet.be> <87mtufw1kh.fsf@gnu.org> <7ab30aad812e5de1216c95b3becb784e3363e615.camel@telenet.be> <87zgycqzfz.fsf@gnu.org> Content-Type: multipart/signed; micalg="pgp-sha512"; protocol="application/pgp-signature"; boundary="=-B/f2LK5SH1auzwQX5K/f" User-Agent: Evolution 3.34.2 MIME-Version: 1.0 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=telenet.be; s=r21; t=1617703005; bh=9PumJZ8JhDKSK4oMiQdzCuIPgUTftNIqOt8tscAGGeQ=; h=Subject:From:To:Cc:Date:In-Reply-To:References; b=Bzjq5aL12xO2hc252nimbtrPuWzGL4wGiz7TycHpIvyo6NP3vNRwYkC3qzGMz39jm QoTW83ROoyn9j2cxIQrIh6AATpyKp5owLMLTpUdXPyqotE8oFtSMXAeZ10DHkq6RIH htFsQ/lkGqtPGhXk9NVPqLzPNbayyyWA1wX+pDfAGbwdOqHuHT+SLfqLqctOFf4GIH tcXGXiqIH/43XP7fX3lc0a5FSuD0xqqcVph4mxjkuG1Ns4EWy6oQuUqiXX/zQPnBnV JoSAkjxINkCcvqoCKj7gJfAFIPqFtS6rrnoMGsisCoTLNpwScS2vrUtIGUQgZOKIZB G76FbH8zf2lAg== X-Spam-Score: -0.7 (/) X-Debbugs-Envelope-To: 47584 Cc: Leo Famulari , 47584@debbugs.gnu.org X-BeenThere: debbugs-submit@debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: debbugs-submit-bounces@debbugs.gnu.org Sender: "Debbugs-submit" X-Spam-Score: -1.7 (-) --=-B/f2LK5SH1auzwQX5K/f Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, 2021-04-05 at 21:54 +0200, Ludovic Court=C3=A8s wrote: > [...] >=20 > OK. It does mean that the bug is hardly exploitable in practice: you > have to be able to log in at all, Yes. > and if you=E2=80=99re able to log in, you have > to log in precisely within the 1s (or less) that follows account > creation, which sounds challenging (TCP + SSH connection establishment > is likely to take as much time or more, Is logging in possible when the home directory doesn't exist? It isn't possible from the console. I guess it isn't possible from SSH either. If it is possible, then the window would be somewhat larger I think. Account creation is done at activation time, while creating home directories is done as a shepherd service (see account-service-type in gnu/system/shadow.scm). > likewise for typing in your password.) An attacker could copy and paste, or have used a single-character password, to save some time. > It=E2=80=99s also one-time chance. Yes. > Do I get it right? I think so, except the window might be larger (but still a one-time chance)= . > Does it warrant as strong messaging as for the recent daemon > =E2=80=98--keep-failed=E2=80=99 vulnerability? As it is a one-time chance, with a limited window, and only under specific circumstances (creating a new user account), I don't think so. But I would still recommend to upgrade. Does the blog post have =E2=80=98too strong me= ssaging=E2=80=99?=20 Greetings, Maxime --=-B/f2LK5SH1auzwQX5K/f Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- iI0EABYKADUWIQTB8z7iDFKP233XAR9J4+4iGRcl7gUCYGwwRxccbWF4aW1lZGV2 b3NAdGVsZW5ldC5iZQAKCRBJ4+4iGRcl7rX2AP0ak8CCNXY2v2apFETUInxpt8UZ 6E0vkWhJvLARcgTkHwEAnnHFIqZOe+EvFa3Ex3qOefhHRIiwFKE8xB0gCdpZsQQ= =oG1p -----END PGP SIGNATURE----- --=-B/f2LK5SH1auzwQX5K/f--