CVE-2023-4421 Explained : Impact and Mitigation

This CVE record was published by Mozilla on December 12, 2023, and it involves a vulnerability in the NSS code used for checking PKCS#1 v1.5 that could lead to Bleichenbacher-like attacks. The affected product is NSS with versions less than 3.61.

Understanding CVE-2023-4421

This section delves into the details of CVE-2023-4421, outlining the vulnerability and its impact.

What is CVE-2023-4421?

The vulnerability in CVE-2023-4421 arises from the NSS code used for checking PKCS#1 v1.5, leaking information that could be exploited in Bleichenbacher-like attacks. This leakage includes the correctness of the padding and the length of the encrypted message through a timing side-channel. An attacker leveraging this vulnerability could decrypt intercepted PKCS#1 v1.5 ciphertexts, such as those from TLS sessions using RSA key exchange, or even forge signatures using the victim's key. The issue was addressed by implementing the implicit rejection algorithm in NSS, ensuring the deterministic random message is returned when invalid padding is detected.

The Impact of CVE-2023-4421

The impact of CVE-2023-4421 is significant, as it exposes a timing side-channel vulnerability in the PKCS#1 v1.5 decryption depadding code. This could allow malicious actors to exploit the timing side-channel leaks to decrypt encrypted messages or forge signatures, posing a serious security risk to affected systems.

Technical Details of CVE-2023-4421

This section focuses on the technical aspects of CVE-2023-4421, including the vulnerability description, affected systems and versions, and the exploitation mechanism.

Vulnerability Description

The vulnerability in CVE-2023-4421 results from the leakage of information in the NSS code used for checking PKCS#1 v1.5, enabling attackers to conduct Bleichenbacher-like attacks by exploiting timing side-channels. The issue was mitigated by implementing the implicit rejection algorithm to prevent such attacks.

Affected Systems and Versions

NSS versions less than 3.61 are impacted by this vulnerability, specifically in the code related to checking PKCS#1 v1.5. Users using affected versions are at risk of exploitation by attackers leveraging timing side-channel leaks.

Exploitation Mechanism

By sending numerous attacker-selected ciphertexts, malicious actors can exploit the timing side-channel leaks in the NSS code to potentially decrypt intercepted PKCS#1 v1.5 ciphertexts or forge signatures using the victim's key. This sophisticated exploitation method underscores the severity of the vulnerability.

Mitigation and Prevention

In light of CVE-2023-4421, it is crucial for organizations and users to take immediate steps to mitigate the risk posed by this vulnerability and implement long-term security practices.

Immediate Steps to Take

Users and organizations utilizing NSS versions older than 3.61 should update to the latest patched version to prevent exploitation of this vulnerability. Additionally, monitoring for any signs of unauthorized decryption attempts or signature forgeries is recommended to detect potential attacks early.

Long-Term Security Practices

To enhance overall security posture, organizations should implement robust security measures, including regular security assessments, threat monitoring, and secure coding practices to prevent similar vulnerabilities from being exploited in the future.

Patching and Updates

Regularly applying security patches and updates for all software components, especially critical libraries like NSS, is essential to address known vulnerabilities and maintain a secure environment. Keeping all systems up to date with the latest security fixes is fundamental in reducing the attack surface and minimizing security risks.