CVE-2023-4421 Information disclosure in NSS
Timing side-channel in NSS PKCS#1 v1.5 padding checks allows attackers to decrypt TLS sessions or forge signatures.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2023-4421?
CVE-2023-4421 is a medium-severity vulnerability in Mozilla NSS, published on 12 Dec 2023. Any signed-in user can exploit it over the network, with no action from the victim.
Official 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.
Weakness: CWE-203
Which versions are affected by CVE-2023-4421?
It affects 1 product.
Products include Mozilla Nss.
How do I fix CVE-2023-4421?
Upgrade to a fixed version.
Is CVE-2023-4421 being exploited?
There is no known exploitation of CVE-2023-4421 in the wild and no public exploit code.
Other vulnerabilities in Mozilla NSS
Sources
Also known as DEBIAN-CVE-2023-4421, GHSA-3hpv-hgvq-792m, OESA-2026-2612, UBUNTU-CVE-2023-4421.