CVE-2020-12413: 
NixOS vulnerability analysis and mitigation

The Raccoon attack (CVE-2020-12413) is a timing vulnerability in the TLS specification that affects HTTPS and other services relying on SSL and TLS 1.2 and below. Discovered in 2020, this vulnerability specifically impacts the Diffie-Hellman (DH) key exchange implementation in TLS. The attack allows attackers under certain conditions to break the encryption and read sensitive communications. The vulnerability primarily affects systems using DHE ciphersuites, particularly those that reuse ephemeral keys (Raccoon Attack).

The vulnerability exploits a timing side-channel in the TLS specification where leading zero bytes in the premaster secret are stripped before being used in further computations. Since the resulting premaster secret is used as input into the key derivation function, which is based on hash functions with different timing profiles, precise timing measurements may enable an attacker to construct an oracle from a TLS server. The vulnerability has been assigned a CVSS v3.1 base score of 5.9 (Medium) with vector CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N (NVD).

If successfully exploited, Raccoon allows attackers to decrypt the connection between users and the server, potentially exposing sensitive information including usernames, passwords, credit card numbers, emails, instant messages, and sensitive documents. The attack requires specific circumstances to be successful, including the server reusing public DH keys and the attacker's ability to execute precise timing measurements (Raccoon Attack).

To mitigate this vulnerability, Mozilla Firefox disabled support for DHE ciphersuites starting from version 78. For server administrators, the primary mitigation is to avoid reusing DH ephemeral keys and to disable support for DHE ciphersuites. Modern versions of OpenSSL (since 1.0.2f) use fresh DH keys by default. TLS 1.3 is not affected by this vulnerability as it preserves leading zero bytes for DHE cipher suites and mandates that keys should not be reused (Mozilla Bug).