CVE-2023-4421: Mozilla Nss

Medium severity, CVSS 6.5. EPSS: 0.8% chance of exploitation in the next 30 days.

The NSS code used for checking PKCS#1 v1.5 was leaking information useful in mounting Bleichenbacher-like attacks. Both the overall correctness of the padding as well as the length of the encrypted message was leaking through timing side-channel. By sending large number of attacker-selected ciphertexts, the attacker would be able to decrypt a previously intercepted PKCS#1 v1.5 ciphertext (for example, to decrypt a TLS session that used RSA key exchange), or forge a signature using the victim's key. The issue was fixed by implementing the implicit rejection algorithm, in which the NSS returns a deterministic random message in case invalid padding is detected, as proposed in the Marvin Attack paper. This vulnerability affects NSS < 3.61.

Affected products

• Mozilla Nss: before 3.6.1 (fixed in 3.6.1)

Published 2023-12-12. Last modified 2026-06-17.