{"cve":"CVE-2023-4421","nvd":{"published":"2023-12-12T17:15:08.347","modified":"2026-06-17T06:37:47.547","status":"Modified","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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N","score":6.5},"cwes":["CWE-203"],"references":["https://bugzilla.mozilla.org/show_bug.cgi?id=1651411","https://www.mozilla.org/security/advisories/mfsa2023-53/","https://bugzilla.mozilla.org/show_bug.cgi?id=1651411","https://lists.debian.org/debian-lts-announce/2023/10/msg00039.html","https://www.mozilla.org/security/advisories/mfsa2023-53/"],"products":["mozilla:nss"],"source":"nvd","synced_at":"2026-10-19T21:42:34.585441961+00:00"},"epss":{"cve":"CVE-2023-4421","score":0.00762,"percentile":0.55369,"date":"2026-11-01"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}