Elevation of Privilege Flaw Impacts Linux Kernel

The Linux kernel is susceptible to a local escalation of privilege impacting the Advanced Linux Sound Architecture (ALSA), Cisco warns.

Tracked as CVE-2017-15265, the vulnerability can be exploited by an attacker to gain elevated privileges on the targeted system. However, because the issue requires local access to the targeted system, the likelihood of a successful exploit is reduced.

“The vulnerability is due to a use-after-free memory error in the ALSA sequencer interface of the affected application. An attacker could exploit this vulnerability by running a crafted application on a targeted system. A successful exploit could allow the attacker to gain elevated privileges on the targeted system,” Cisco explains in an advisory published on Friday, October 13.

Discovered by Michael23 Yu and already confirmed by Kernel.org, the bug starts with a potential race window that opens when creating and deleting a port via ioctl.

The issue is that snd_seq_create_port() creates the port object and returns its pointer, but can be deleted immediately by another thread because it doesn’t take the refcount. snd_seq_ioctl_create_port() still calls for snd_seq_system_client_ev_port_start() with the created port object being deleted, thus triggering the use-after-free.

A patch has been already published on the ALSA project’s website: “it’s fixed simply by taking the refcount properly at snd_seq_create_port() and letting the caller unref the object after use.  Also, there is another potential use-after-free by sprintf() call in snd_seq_create_port(), and this is moved inside the lock.”

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