CVE-2023-6871Network attack vector

External protocol launch via skipped warning

Published Dec 19, 2023 · Updated Aug 2, 2024

Improper UI warning in Mozilla Firefox before 121 allows context-dependent attackers to open an external protocol handler without confirmation. The _hasProtocolHandlerPermission check treated system-principal navigation from the address bar or other browser UI as already permitted, reducing the expected prompt count from one to zero for a new external scheme. A user must navigate to an attacker-influenced external-scheme URL; the handler can launch without the warning intended to flag unusual or dangerous actions.

CVSS severity4.3
Medium
EPSS probability0.49%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper UI warning in Mozilla Firefox before 121 allows context-dependent attackers to open an external protocol handler without confirmation. The _hasProtocolHandlerPermission check treated system-principal navigation from the address bar or other browser UI as already permitted, reducing the expected prompt count from one to zero for a new external scheme. A user must navigate to an attacker-influenced external-scheme URL; the handler can launch without the warning intended to flag unusual or dangerous actions.

The record

CVE
CVE-2023-6871
Published
Dec 19, 2023
Updated
Aug 2, 2024
Vendor
Mozilla
Product
Firefox
Classifications
T1204
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 19, 2023CVE publishedPublication date reported by the CVE source.
  2. Aug 2, 2024Record 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 <121

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=unspecified <121

Published CVSS scores

4.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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

T1204User Execution

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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