CVE-2023-6209Public exploitNetwork attack vector

Host override via triple-slash URL path collapse

Published Nov 21, 2023 · Updated Feb 13, 2025

URL parsing in Mozilla Firefox before 120, Firefox ESR before 115.5.0, and Thunderbird before 115.5 allows remote attackers to override a URL host. The networking parser treats a three-slash relative URL as an empty host, collapses a /../ segment, then uses the remaining path term as the host. A user must follow attacker-controlled web content; host substitution can redirect the request to an attacker-chosen site, while Thunderbird mail reading disables scripting by default.

CVSS severity6.5
Medium
EPSS probability1.41%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

URL parsing in Mozilla Firefox before 120, Firefox ESR before 115.5.0, and Thunderbird before 115.5 allows remote attackers to override a URL host. The networking parser treats a three-slash relative URL as an empty host, collapses a /../ segment, then uses the remaining path term as the host. A user must follow attacker-controlled web content; host substitution can redirect the request to an attacker-chosen site, while Thunderbird mail reading disables scripting by default.

The record

CVE
CVE-2023-6209
Published
Nov 21, 2023
Updated
Feb 13, 2025
Vendor
Mozilla
Product
Firefox
Classifications
CWE-22, T1204.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 21, 2023CVE publishedPublication date reported by the CVE source.
  2. Feb 13, 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 <120

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=unspecified <120
Mozilla · Thunderbirdversion=unspecified <115.5
Mozilla · Firefox ESRversion=unspecified <115.5.0

Published CVSS scores

6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/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.

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 exploitPublished

Weakness, pattern, technique

CWE-22Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
T1204.001User Execution: Malicious Link

Public exploit references

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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