PatchTheCVECVE-2023-4421: The NSS code used for checking PKCS#1 v1.5 was leaking information useful in mounting Bleichenbacher-like atta
CVE-2023-4421 is a medium-severity flaw (CVSS 6.5) affecting nss. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
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 ex
Why this priority
- No elevated risk signals yet
A fixed release or distro patch exists.
Risk facts
| CVSS score | 6.5 (Medium) |
| Attack vector | Network (remote) |
| Attack complexity | Low |
| Privileges needed | Low |
| User interaction | None |
| EPSS exploit chance | 0.8% (top 45%) |
| CISA exploited list | No |
| Weakness | CWE-203 |
| Published | 2023-12-12 |
| Last modified | 2026-06-17 |
Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score
Am I affected?
Timeline
- Published CVE record published
- Updated Record last modified
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.
Quick answers
How do I fix CVE-2023-4421?
nss: upgrade to 3.6.1. Exact commands for each OS are on this page.
Is CVE-2023-4421 being exploited?
CVE-2023-4421 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.
What does CVE-2023-4421 affect?
CVE-2023-4421 affects nss. Severity is medium (CVSS 6.5). 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-ch
How urgent is CVE-2023-4421?
Priority 37/100. No elevated risk signals yet.
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