Mozilla Foundation Security Advisory 2023-53
Timing side-channel in PKCS#1 v1.5 decryption depadding code
- Announced
- December 12, 2023
- Impact
- moderate
- Products
- NSS
- Fixed in
-
- NSS 3.61
Although this issue was embargoed until 2023, it was fixed in NSS 3.61 as released on January 22, 2021
#CVE-2023-4421: Timing side-channel in PKCS#1 v1.5 decryption depadding code
- Reporter
- Hubert Kario
- Impact
- moderate
Description
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.