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FreeBSD-SA-20:14.sctp Security Advisory
The FreeBSD Project

Topic: Improper checking in SCTP-AUTH shared key update

Category: core
Module: kernel
Announced: 2020-05-12
Credits: da_cheng_shao@yeah.net
Affects: FreeBSD 11.3
Corrected: 2019-09-19 10:01:19 UTC (stable/12, 12.1-STABLE)
2019-09-19 10:06:18 UTC (stable/11, 11.3-STABLE)
2020-05-12 16:55:32 UTC (releng/11.3, 11.3-RELEASE-p9)
CVE Name: CVE-2019-15878

Note: The upcoming release of FreeBSD 11.4 was branched after the original
commit to the stable branch and already includes the fix for this advisory.
Similarly, the 12.1 branch was created shortly after the original commit to
the stable branch and already includes the fix.

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:https://security.FreeBSD.org/>.

I. Background

The Stream Control Transmission Protocol (SCTP) is a transport protocol
supporting the socket API. An SCTP packet consists of an SCTP common header
and a number of SCTP chunks.

The SCTP extension SCTP-AUTH can be used to authenticate SCTP chunks. It
uses shared keys which can be managed via the socket API by the application
using an SCTP association.

II. Problem Description

The SCTP layer does improper checking when an application tries to update
a shared key. Therefore an unprivileged local user can trigger a use-after-
free situation, for example by specific sequences of updating shared keys and
closing the SCTP association.

III. Impact

Triggering the use-after-free situation may result in unintended kernel
behaviour including a kernel panic.

IV. Workaround

No workaround is available.

V. Solution

Upgrade your vulnerable system to a supported FreeBSD stable or
release / security branch (releng) dated after the correction date,
and reboot.

Perform one of the following:

1) To update your vulnerable system via a binary patch:

Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install
# shutdown -r +10min “Rebooting for a security update”

2) To update your vulnerable system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch https://security.FreeBSD.org/patches/SA-20:14/sctp.patch
# fetch https://security.FreeBSD.org/patches/SA-20:14/sctp.patch.asc
# gpg –verify sctp.patch.asc

b) Apply the patch. Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile your kernel as described in
<URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

VI. Correction details

The following list contains the correction revision numbers for each
affected branch.

Branch/path Revision
– ————————————————————————-
stable/12/ r352509
stable/11/ r352509
releng/11.3/ r360975
– ————————————————————————-

To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:

# svn diff -cNNNNNN –summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-15878>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-20:14.sctp.asc>
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