CVE-2023-4421: Mozilla NSS · Timing side-channel in PKCS#1 v1.5 decryption depadding code
Affects Mozilla NSSSource CVE Database V5
Not known to be exploited : upgrade to 3.61 when convenient.
Data as of 25 Oct 2026, 21:42 UTC
Rated by Threat Radar · No CVSS score from NVD or the CNA
- EPSS
- 0.7% chance of exploitation in 30 days – higher than 55% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available – fixed in 3.61
Exploitation evidence
Disclosed: evidence found.
CVE published 12 Dec 2023
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 2026-10-25.
What to do
Upgrade Mozilla NSS to 3.61.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| Mozilla NSS | Affected
| Fixed in
|
AI-suggested
This vulnerability is fixed in Mozilla NSS version 3.61. Users and administrators should upgrade to NSS 3.61 or later to mitigate this issue.
Description
A timing side-channel vulnerability exists in the PKCS#1 v1.5 decryption depadding code of Mozilla NSS versions prior to 3.61. This flaw leaks information about padding correctness and encrypted message length, enabling Bleichenbacher-like attacks. An attacker can exploit this by sending many crafted ciphertexts to decrypt intercepted ciphertexts or forge signatures. The issue is fixed in NSS 3.61 by implementing an implicit rejection algorithm that returns deterministic random messages on invalid padding detection.