Pierluigi Paganini March 25, 2021

The OpenSSL Project addresses two high-severity vulnerabilities, including one related to verifying a certificate chain and one that can trigger a DoS condition.

The OpenSSL Project this week released version 1.1.1k to address two high-severity vulnerabilities, respectively tracked as CVE-2021-3450 and CVE-2021-3449.

The CVE-2021-3449 vulnerability could be exploited to trigger a DoS condition by sending a specially crafted renegotiation ClientHello message from a client.

“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,” State the advisory.

The issue affects servers running OpenSSL 1.1.1 versions with TLS 1.2 and renegotiation enabled, which is the default configuration. The vulnerability was reported by Peter Kästle and Samuel Sapalski from Nokia.

The CVE-2021-3450 vulnerability is related to the verification of a certificate chain when using the X509_V_FLAG_X509_STRICT flag.

“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.” reads the advisory published by the OpenSSL Project. “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,”

The vulnerability was reported by Benjamin Kaduk and Xiang Ding from Akamai.

In February 2021, the OpenSSL Project released security patches to address three vulnerabilities, two denial-of-service (DoS) flaws, and an incorrect SSLv2 rollback protection issue.

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Pierluigi Paganini

(SecurityAffairs – hacking, OpenSSL Project)

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