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FreeBSD-SA-20:11.openssl Security Advisory
The FreeBSD Project

Topic: OpenSSL remote denial of service vulnerability

Category: contrib
Module: openssl
Announced: 2020-04-21
Credits: Bernd Edlinger
Affects: FreeBSD 12.1
Corrected: 2020-04-21 15:47:58 UTC (stable/12, 12.1-STABLE)
2020-04-21 15:53:08 UTC (releng/12.1, 12.1-RELEASE-p4)
CVE Name: CVE-2020-1967

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

FreeBSD includes software from the OpenSSL Project. The OpenSSL Project is a
collaborative effort to develop a robust, commercial-grade, full-featured
Open Source toolkit for the Transport Layer Security (TLS) and Secure Sockets
Layer (SSL) protocols. It is also a full-strength general purpose
cryptography library.

II. Problem Description

Server or client applications that call the SSL_check_chain() function during
or after a TLS 1.3 handshake may crash due to a NULL pointer dereference as a
result of incorrect handling of the “signature_algorithms_cert” TLS
extension. The crash occurs if an invalid or unrecognized signature
algorithm is received from the peer.

III. Impact

A malicious peer could exploit the NULL pointer dereference crash, causing a
denial of service attack.

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
# 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-20:11/openssl.patch
# fetch https://security.FreeBSD.org/patches/SA-20:11/openssl.patch.asc
# gpg –verify openssl.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/ r360147
releng/12.1/ r360150
– ————————————————————————-

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://www.openssl.org/news/secadv/20200421.txt>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-1967>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-20:11.openssl.asc>
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