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Published: 15 March 2022

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. Fixed in OpenSSL 3.0.2 (Affected 3.0.0,3.0.1). Fixed in OpenSSL 1.1.1n (Affected 1.1.1-1.1.1m). Fixed in OpenSSL 1.0.2zd (Affected 1.0.2-1.0.2zc).



Cvss 3 Severity Score


Score breakdown


Package Release Status
Launchpad, Ubuntu, Debian
bionic Needs triage

focal Needs triage

impish Ignored
(end of life)
trusty Does not exist

upstream Needs triage

xenial Needs triage

jammy Needs triage

kinetic Not vulnerable
lunar Not vulnerable
Launchpad, Ubuntu, Debian
bionic Not vulnerable
(uses system openssl1.0)
focal Not vulnerable
(uses system openssl1.1)
impish Not vulnerable
(uses system openssl1.1)
trusty Not vulnerable
(uses system openssl)
upstream Needs triage

xenial Not vulnerable
(uses system openssl)
jammy Needed

kinetic Not vulnerable
(uses system openssl1.1)
lunar Not vulnerable
(uses system openssl1.1)
Launchpad, Ubuntu, Debian
Released (1.1.1-1ubuntu2.1~18.04.15)
Released (1.1.1f-1ubuntu2.12)
Released (1.1.1l-1ubuntu1.2)
Released (1.1.1n,3.0.2)
Released (3.0.2-0ubuntu1)
Released (3.0.2-0ubuntu1)
Released (3.0.2-0ubuntu1)
Launchpad, Ubuntu, Debian
Released (1.0.2n-1ubuntu5.8)
focal Does not exist

impish Does not exist

trusty Does not exist

upstream Needs triage

xenial Does not exist

jammy Does not exist

kinetic Does not exist

lunar Does not exist

Severity score breakdown

Parameter Value
Base score 7.5
Attack vector Network
Attack complexity Low
Privileges required None
User interaction None
Scope Unchanged
Confidentiality None
Integrity impact None
Availability impact High
Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H