CVE-2023-4421Network attack vector

Decryption and signature forgery via depadding timing oracle

Published Dec 12, 2023 · Updated Nov 4, 2025

Timing side channel in Mozilla NSS before 3.61 allows remote attackers to decrypt intercepted PKCS#1 v1.5 ciphertexts via timing queries. The PKCS#1 v1.5 depadding path returns distinguishable timing for invalid padding and message lengths instead of using implicit rejection. A reachable server-side RSA operation and many attacker-selected ciphertexts are required; the oracle also enables signature forgery.

CVSS severity6.5
Medium
EPSS probability0.76%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Timing side channel in Mozilla NSS before 3.61 allows remote attackers to decrypt intercepted PKCS#1 v1.5 ciphertexts via timing queries. The PKCS#1 v1.5 depadding path returns distinguishable timing for invalid padding and message lengths instead of using implicit rejection. A reachable server-side RSA operation and many attacker-selected ciphertexts are required; the oracle also enables signature forgery.

The record

CVE
CVE-2023-4421
Published
Dec 12, 2023
Updated
Nov 4, 2025
Vendor
Mozilla
Product
Network Security Services (NSS)
Classifications
CWE-203, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 12, 2023CVE publishedPublication date reported by the CVE source.
  2. Nov 4, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <3.61

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Network Security Services (NSS)version=unspecified <3.61

Published CVSS scores

5.9SUSECVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-203Observable Discrepancy
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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