Information Exposure Affecting nss package, versions <2:3.42.1-1+deb10u7

Note: Versions mentioned in the description apply only to the upstream nss package and not the nss package as distributed by Debian. See How to fix? for Debian:10 relevant fixed versions and status.

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.

• https://security-tracker.debian.org/tracker/CVE-2023-4421
• https://bugzilla.mozilla.org/show_bug.cgi?id=1651411
• https://www.mozilla.org/security/advisories/mfsa2023-53/