#VU8201 Privilege escalation in NetBSD

Vulnerability identifier: #VU8201

Vulnerability risk: Low

CVSSv4.0: 5.9 [CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/U:Clear]

CVE-ID: N/A

CWE-ID: CWE-122

Exploitation vector: Local

Exploit availability: No

Vulnerable software:
NetBSD
Operating systems & Components / Operating system

Vendor: NetBSD Foundation, Inc

Description

The vulnerability allows a local user to escalate privileges on the system.

The vulnerability exists due to Vnode reference leak in the openat system call. When calling the openat system call using a file descriptor that does not name a directory as the starting point for path lookup, a reference to the underlying vnode is taken temporarily and then not released when the error is discovered. Performing such a call often enough results in overflowing the internal reference count and corrupting the kernel heap.

Successful exploitation of the vulnerability may allow an attacker to gain root access to the affected system.

Mitigation
The fixed source may be obtained from the NetBSD CVS repository.
The following instructions briefly summarise how to upgrade your
kernel. In these instructions, replace:

  ARCH     with your architecture (from uname -m),
  KERNCONF with the name of your kernel configuration file and
  VERSION  with the file version below

File versions containing the fixes:

FILE  HEAD   netbsd-8   netbsd-7   netbsd-7-1   netbsd-7-0
----  ----   --------   --------   ----------   ----------
sys/kern/vfs_lookup.c
       1.208  1.207.2.1  1.201.4.1  1.201.12.1   1.201.8.1

To update from CVS, re-build, and re-install the kernel:

# cd src
# cvs update -d -P -r VERSION sys/kern/vfs_lookup.c
# ./build.sh kernel=KERNCONF
# mv /netbsd /netbsd.old
# cp sys/arch/ARCH/compile/obj/KERNCONF/netbsd /netbsd
# shutdown -r now

Vulnerable software versions

NetBSD: 6.0 - 7.0.2

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External links
https://ftp.netbsd.org/pub/NetBSD/security/advisories/NetBSD-SA2017-006.txt.asc

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Q & A

Can this vulnerability be exploited remotely?

No. This vulnerability can be exploited locally. The attacker should have authentication credentials and successfully authenticate on the system.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.