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.

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - 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. (CVE-2023-4421)

Note that Nessus relies on the presence of the package as reported by the vendor.

The version of nss-softokn installed on the remote host is prior to 3.67.0-3. It is, therefore, affected by a vulnerability as referenced in the ALAS2-2025-2835 advisory.

    new tlsfuzzer code can still detect timing issues in RSA operations (CVE-2023-4421)

Tenable has extracted the preceding description block directly from the tested product security advisory.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

An update of the nss package has been released.

The remote Ubuntu 20.04 LTS / 22.04 LTS / 23.10 host has packages installed that are affected by multiple vulnerabilities as referenced in the USN-6727-1 advisory.

    It was discovered that NSS incorrectly handled padding when checking PKCS#1 certificates. A remote     attacker could possibly use this issue to perform Bleichenbacher-like attacks and recover private data.
    This issue only affected Ubuntu 20.04 LTS. (CVE-2023-4421)

    It was discovered that NSS had a timing side-channel when performing RSA decryption. A remote attacker     could possibly use this issue to recover private data. (CVE-2023-5388)

    It was discovered that NSS had a timing side-channel when using certain NIST curves. A remote attacker     could possibly use this issue to recover private data. (CVE-2023-6135)

    The NSS package contained outdated CA certificates. This update refreshes the NSS package to version 3.98     which includes the latest CA certificate bundle and other security improvements.

Tenable has extracted the preceding description block directly from the Ubuntu security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The remote Debian 10 host has packages installed that are affected by multiple vulnerabilities as referenced in the dla-3634 advisory.

    -------------------------------------------------------------------------     Debian LTS Advisory DLA-3634-1                debian-lts@lists.debian.org     https://www.debian.org/lts/security/                         Sean Whitton     October 28, 2023                              https://wiki.debian.org/LTS
    -------------------------------------------------------------------------

    Package        : nss     Version        : 2:3.42.1-1+deb10u7     CVE ID         : CVE-2020-25648 CVE-2023-4421

    Multiple vulnerabilities were found in nss, a set of libraries designed     to support cross-platform development of security-enabled client and     server applications.

    CVE-2020-25648

        A flaw was discovered in how NSS handles CipherChangeSpec messages         in TLS 1.3.  It could allow an attacker to send multiple CCS         messages to servers compiled against NSS, causing denial-of-service.

    CVE-2023-4421

        A fuzzing project discovered vulnerabilities to Bleichenbacher         timing attacks in NSS's facilities for RSA cryptography.

    For Debian 10 buster, these problems have been fixed in version     2:3.42.1-1+deb10u7.

    We recommend that you upgrade your nss packages.

    For the detailed security status of nss please refer to     its security tracker page at:
    https://security-tracker.debian.org/tracker/nss

    Further information about Debian LTS security advisories, how to apply     these updates to your system and frequently asked questions can be     found at: https://wiki.debian.org/LTS     Attachment:
    signature.asc     Description: PGP signature

Tenable has extracted the preceding description block directly from the Debian security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The version of nss-softokn installed on the remote host is prior to 3.53.1-6.48. It is, therefore, affected by a vulnerability as referenced in the ALAS-2023-1858 advisory.

    new tlsfuzzer code can still detect timing issues in RSA operations (CVE-2023-4421)

Tenable has extracted the preceding description block directly from the tested product security advisory.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

ID	Name	Product	Family	Severity
246644	Linux Distros Unpatched Vulnerability : CVE-2023-4421	Nessus	Misc.	medium
235073	Amazon Linux 2 : nss-softokn (ALAS-2025-2835)	Nessus	Amazon Linux Local Security Checks	medium
204001	Photon OS 3.0: Nss PHSA-2024-3.0-0716	Nessus	PhotonOS Local Security Checks	medium
193171	Ubuntu 20.04 LTS / 22.04 LTS / 23.10 : NSS vulnerabilities (USN-6727-1)	Nessus	Ubuntu Local Security Checks	medium
183996	Debian dla-3634 : libnss3 - security update	Nessus	Debian Local Security Checks	medium
183847	Amazon Linux AMI : nss-softokn (ALAS-2023-1858)	Nessus	Amazon Linux Local Security Checks	medium

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CVE-2023-4421

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