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Case File

CVE-2023-4421

MEDIUM · CVSS 6.5 EPSS 0.63%

Source: NVD + CISA KEV + EPSS (historical backfill) · Published 2023-12-12 · Last synced 2026-08-04

CyberRota Analysis

This is a medium severity vulnerability with a CVSS score of 6.5. It affects Exchange.

CVE
CVE-2023-4421
Severity
MEDIUM
CVSS
6.5
EPSS
0.63%
Exchange

Original NVD 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. This vulnerability affects NSS < 3.61.

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