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Date: Wed, 5 Feb 2020 10:59:55 +0100
From: Riccardo Schirone <rschiron@...hat.com>
To: oss-security@...ts.openwall.com
Subject: CVE-2020-1712 systemd: use-after-free when asynchronous polkit
 queries are performed

Hello,

A heap use-after-free vulnerability was found in systemd, when asynchronous
Polkit queries are performed while handling Dbus messages. A local unprivileged
attacker can abuse this flaw to crash systemd services or potentially execute
code and elevate their privileges, by sending specially crafted Dbus messages.

CVE-2020-1712 has been assigned to this issue.

This flaw happens due to the way bus_verify_polkit_async() works. Some DBus
interfaces use a cache to store objects for a short period and they clear it as
soon as the bus is again in the idle state. However, if a DBus method uses
bus_verify_polkit_async(), the method may have to wait a while until the polkit
action is resolved and when that happens the method handler is called again,
with the userdata previously allocated. If the polkit request takes too long,
the clearing of the cache would free the stored objects before the method is
called the second time, causing the use-after-free vulnerability.

The issue was reported by Tavis Ormandy, Google Project Zero.

Upstream fix is included in v245-rc1:
https://github.com/systemd/systemd/commit/ea0d0ede03c6f18dbc5036c5e9cccf97e415ccc2

Thanks,
-- 
Riccardo Schirone
Red Hat -- Product Security
Email: rschiron@...hat.com
PGP-Key ID: CF96E110

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