OpenSSL Security Advisory

Matt Caswell matt at
Tue Mar 15 16:41:15 UTC 2022

Hash: SHA256

OpenSSL Security Advisory [15 March 2022]

Infinite loop in BN_mod_sqrt() reachable when parsing certificates (CVE-2022-0778)

Severity: High

The BN_mod_sqrt() function, which computes a modular square root, contains
a bug that can cause it to loop forever for non-prime moduli.

Internally this function is used when parsing certificates that contain
elliptic curve public keys in compressed form or explicit elliptic curve
parameters with a base point encoded in compressed form.

It is possible to trigger the infinite loop by crafting a certificate that
has invalid explicit curve parameters.

Since certificate parsing happens prior to verification of the certificate
signature, any process that parses an externally supplied certificate may thus
be subject to a denial of service attack. The infinite loop can also be
reached when parsing crafted private keys as they can contain explicit
elliptic curve parameters.

Thus vulnerable situations include:

 - TLS clients consuming server certificates
 - TLS servers consuming client certificates
 - Hosting providers taking certificates or private keys from customers
 - Certificate authorities parsing certification requests from subscribers
 - Anything else which parses ASN.1 elliptic curve parameters

Also any other applications that use the BN_mod_sqrt() where the attacker
can control the parameter values are vulnerable to this DoS issue.

In the OpenSSL 1.0.2 version the public key is not parsed during initial
parsing of the certificate which makes it slightly harder to trigger
the infinite loop. However any operation which requires the public key
from the certificate will trigger the infinite loop. In particular the
attacker can use a self-signed certificate to trigger the loop during
verification of the certificate signature.

This issue affects OpenSSL versions 1.0.2, 1.1.1 and 3.0.  It was
addressed in the releases of 1.1.1n and 3.0.2 on the 15th March 2022.

OpenSSL 1.0.2 users should upgrade to 1.0.2zd (premium support customers only)
OpenSSL 1.1.1 users should upgrade to 1.1.1n
OpenSSL 3.0 users should upgrade to 3.0.2

This issue was reported to OpenSSL on the 24th February 2022 by Tavis Ormandy
from Google. The fix was developed by David Benjamin from Google and Tomáš Mráz
from OpenSSL.


OpenSSL 1.0.2 is out of support and no longer receiving public updates. Extended
support is available for premium support customers:

OpenSSL 1.1.0 is out of support and no longer receiving updates of any kind.
It is affected by the issue.

Users of these versions should upgrade to OpenSSL 3.0 or 1.1.1.


URL for this Security Advisory:

Note: the online version of the advisory may be updated with additional details
over time.

For details of OpenSSL severity classifications please see:


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