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FreeBSD-SA-20:01.libfetch Security Advisory
The FreeBSD Project

Topic: libfetch buffer overflow

Category: core
Module: libfetch
Announced: 2020-01-28
Credits: Duncan Overbruck
Affects: All supported versions of FreeBSD.
Corrected: 2020-01-28 18:40:55 UTC (stable/12, 12.1-STABLE)
2020-01-28 18:55:25 UTC (releng/12.1, 12.1-RELEASE-p2)
2020-01-28 18:55:25 UTC (releng/12.0, 12.0-RELEASE-p13)
2020-01-28 18:42:06 UTC (stable/11, 11.3-STABLE)
2020-01-28 18:55:25 UTC (releng/11.3, 11.3-RELEASE-p6)
CVE Name: CVE-2020-7450

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

libfetch(3) is a multi-protocol file transfer library included with FreeBSD
and used by the fetch(1) command-line tool, pkg(8) package manager, and
others.

II. Problem Description

A programming error allows an attacker who can specify a URL with a username
and/or password components to overflow libfetch(3) buffers.

III. Impact

An attacker in control of the URL to be fetched (possibly via HTTP redirect)
may cause a heap buffer overflow, resulting in program misbehavior or
malicious code execution.

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.

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

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-20:01/libfetch.patch
# fetch https://security.FreeBSD.org/patches/SA-20:01/libfetch.patch.asc
# gpg –verify libfetch.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 all daemons that use the library, or reboot the system.

VI. Correction details

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

Branch/path Revision
– ————————————————————————-
stable/12/ r357213
releng/12.1/ r357217
releng/12.0/ r357217
stable/11/ r357214
releng/11.3/ r357217
– ————————————————————————-

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-2020-7450>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-20:01.libfetch.asc>
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