Arch Linux Security Advisory ASA-202103-10
==========================================

Severity: High
Date    : 2021-03-25
CVE-ID  : CVE-2021-3449 CVE-2021-3450
Package : openssl
Type    : multiple issues
Remote  : Yes
Link    : https://security.archlinux.org/AVG-1736

Summary
=======

The package openssl before version 1.1.1.k-1 is vulnerable to multiple
issues including certificate verification bypass and denial of service.

Resolution
==========

Upgrade to 1.1.1.k-1.

# pacman -Syu "openssl>=1.1.1.k-1"

The problems have been fixed upstream in version 1.1.1.k.

Workaround
==========

None.

Description
===========

- CVE-2021-3449 (denial of service)

An OpenSSL TLS server may crash if sent a maliciously crafted
renegotiation ClientHello message from a client. If a TLSv1.2
renegotiation ClientHello omits the signature_algorithms extension
(where it was present in the initial ClientHello), but includes a
signature_algorithms_cert extension then a NULL pointer dereference
will result, leading to a crash and a denial of service attack.

A server is only vulnerable if it has TLSv1.2 and renegotiation enabled
(which is the default configuration). OpenSSL TLS clients are not
impacted by this issue.

All OpenSSL 1.1.1 versions are affected by this issue. Users of these
versions should upgrade to OpenSSL 1.1.1k.

- CVE-2021-3450 (certificate verification bypass)

The X509_V_FLAG_X509_STRICT flag enables additional security checks of
the certificates present in a certificate chain. It is not set by
default.

Starting from OpenSSL version 1.1.1h a check to disallow certificates
in the chain that have explicitly encoded elliptic curve parameters was
added as an additional strict check.

An error in the implementation of this check meant that the result of a
previous check to confirm that certificates in the chain are valid CA
certificates was overwritten. This effectively bypasses the check that
non-CA certificates must not be able to issue other certificates.

If a "purpose" has been configured then there is a subsequent
opportunity for checks that the certificate is a valid CA.  All of the
named "purpose" values implemented in libcrypto perform this check.
Therefore, where a purpose is set the certificate chain will still be
rejected even when the strict flag has been used. A purpose is set by
default in libssl client and server certificate verification routines,
but it can be overridden or removed by an application.

In order to be affected, an application must explicitly set the
X509_V_FLAG_X509_STRICT verification flag and either not set a purpose
for the certificate verification or, in the case of TLS client or
server applications, override the default purpose.

OpenSSL versions 1.1.1h and newer are affected by this issue. Users of
these versions should upgrade to OpenSSL 1.1.1k.

Impact
======

A malicious client can crash the server, or a malicious server can
serve a crafted certificate to bypass certificate verification
routines.

References
==========

https://www.openssl.org/news/secadv/20210325.txt
https://git.openssl.org/?p=openssl.git;a=commitdiff;h=fb9fa6b51defd48157eeb207f52181f735d96148
https://git.openssl.org/?p=openssl.git;a=commitdiff;h=2a40b7bc7b94dd7de897a74571e7024f0cf0d63b
https://security.archlinux.org/CVE-2021-3449
https://security.archlinux.org/CVE-2021-3450