Here is more details are reported by OpenVas:
Summary
The SSL/TLS service uses Diffie-Hellman groups with insufficient strength (key size < 2048).
Detection Result
Server Temporary Key Size: 1024 bits
Insight
The Diffie-Hellman group are some big numbers that are used as base for the DH computations. They can be, and often are, fixed. The security of the final secret depends on the size of these parameters. It was found that 512 and 768 bits to be weak, 1024 bits to be breakable by really powerful attackers like governments.
Detection Method
Checks the DHE temporary public key size.
| Details: | SSL/TLS: Diffie-Hellman Key Exchange Insufficient DH Group Strength Vu… OID: 1.3.6.1.4.1.25623.1.0.106223 |
|---|---|
| Version used: | 2023-07-21T05:05:22Z |
Impact
An attacker might be able to decrypt the SSL/TLS communication offline.
Solution
Solution Type:
Workaround
Deploy (Ephemeral) Elliptic-Curve Diffie-Hellman (ECDHE) or use a 2048-bit or stronger Diffie-Hellman group (see the references). For Apache Web Servers: Beginning with version 2.4.7, mod_ssl will use DH parameters which include primes with lengths of more than 1024 bits.