FL MGUARD and TC MGUARD devices are affected by a possible infinite loop within a OpenSSL library method for parsing elliptic curve parameters. This method is used on parsing cryptographic certificates that contain elliptic curve public keys in compressed form, which may occur on:

• Parsing client certificates for HTTPS administrative login
• Parsing client certificates for SSH administrative login
• Parsing peer certificates for IPsec VPN connections
• Parsing certificates of external servers, including:
  • OpenVPN server
  • Configuration pull server
  • Update server

Attackers could try to exploit the vulnerability from remote.
For the mGuard Device Manager only the mdm Installer for Windows is affected.

UPDATE A: Added FL MGUARD 1102 and FL MGUARD 1105:

On FL MGUARD 1102 and FL MGUARD 1105 with mGuardNT 1.5.2 and older, the device can
be affected through an adapted certificate. This can occur on connection with a remote logging
server, configured for certificate authentication, or an remote authentication server at certificate
based authentication.

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).