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FreeBSD-SA-20:30.ftpd Security Advisory
The FreeBSD Project

Topic: ftpd privilege escalation via ftpchroot feature

Category: core
Module: ftpd
Announced: 2020-09-15
Credits: Anonymous working with Trend Micro Zero Day Initiative
Affects: All supported versions of FreeBSD.
Corrected: 2020-09-15 20:55:13 UTC (stable/12, 12.2-STABLE)
2020-09-15 21:47:44 UTC (releng/12.2, 12.2-BETA1-p1)
2020-09-15 21:47:44 UTC (releng/12.1, 12.1-RELEASE-p10)
2020-09-15 20:56:14 UTC (stable/11, 11.4-STABLE)
2020-09-15 21:47:44 UTC (releng/11.4, 11.4-RELEASE-p4)
2020-09-15 21:47:44 UTC (releng/11.3, 11.3-RELEASE-p14)
CVE Name: CVE-2020-7468

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

ftpd(8) is a daemon that implements an FTP server. To restrict
filesystem access of authenticated clients, ftpd(8) supports the
ftpchroot(5) feature, which allows the system administrator to designate
a root directory for each FTP user. This is implemented using the
chroot(2) system call.

II. Problem Description

A ftpd(8) bug in the implementation of the file system sandbox, combined
with capabilities available to an authenticated FTP user, can be used to
escape the file system restriction configured in ftpchroot(5).
Moreover, the bug allows a malicious client to gain root privileges.

III. Impact

A malicious FTP user can gain privileged access to an affected system.

IV. Workaround

No workaround is available. Systems not running ftpd(8) or not making
use of ftpchroot(5) are not affected. Exploitation of the bug requires
that a malicious FTP client have login access to the server. Anonymous
access is not sufficient.

V. Solution

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

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

Restart the applicable daemons, or reboot the system.

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-20:30/ftpd.patch
# fetch https://security.FreeBSD.org/patches/SA-20:30/ftpd.patch.asc
# gpg –verify ftpd.patch.asc

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

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

c) Recompile the operating system using buildworld and installworld as
described in <URL:https://www.FreeBSD.org/handbook/makeworld.html>.

Restart the applicable daemons, or reboot the system.

VI. Correction details

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

Branch/path Revision
– ————————————————————————-
stable/12/ r365772
releng/12.2/ r365781
releng/12.1/ r365781
stable/11/ r365773
releng/11.4/ r365781
releng/11.3/ r365781
– ————————————————————————-

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-2020-7468>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-20:30.ftpd.asc>
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