CVE-2022-34476Network attack vector

Malformed ASN.1 acceptance via reused end marker

Published Dec 22, 2022 · Updated Apr 15, 2025

Improper ASN.1 validation in Mozilla Firefox before 102 allows remote attackers to make the NSS decoder accept crafted malformed input. While decoding an indefinite-length SEQUENCE within an indefinite-length GROUP, the parser treats one end-of-contents marker as terminating both containers. The condition reaches a legacy decoder not used for WebPKI certificates, and Mozilla demonstrated no consequence beyond accepting an item with a missing trailing marker.

CVSS severity9.8
Critical
EPSS probability0.70%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper ASN.1 validation in Mozilla Firefox before 102 allows remote attackers to make the NSS decoder accept crafted malformed input. While decoding an indefinite-length SEQUENCE within an indefinite-length GROUP, the parser treats one end-of-contents marker as terminating both containers. The condition reaches a legacy decoder not used for WebPKI certificates, and Mozilla demonstrated no consequence beyond accepting an item with a missing trailing marker.

The record

CVE
CVE-2022-34476
Published
Dec 22, 2022
Updated
Apr 15, 2025
Vendor
Mozilla
Product
Firefox
Classifications
CWE-20
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 22, 2022CVE publishedPublication date reported by the CVE source.
  2. Apr 15, 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 <102

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=unspecified <102

Published CVSS scores

9.8CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

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-20Improper Input Validation

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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