dbcve.org
FirefoxWeb browser · Mozilla

CVE-2023-6209

MEDIUM · 6.5 CVSS v3.1 Published 2023-11-21
Fix available
A fix is available. Upgrade to 115.5 / 115.5.0 or later.
See remediation →
72/100
Remediation priority · Elevated
Remotely reachable No privileges

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Relative URLs starting with three slashes were incorrectly parsed, and a path-traversal "/../" part in the path could be used to override the specified host. This could contribute to security problems in web sites. This vulnerability affects Firefox < 120, Firefox ESR < 115.5.0, and Thunderbird < 115.5.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Mozilla products incorrectly parsed relative URLs starting with three slashes, allowing path-traversal '/../' sequences in the path to override the specified host. This URL parsing flaw could be exploited to bypass security checks or contribute to other web security issues.

MitigationUpdate to the fixed versions: Firefox 120 or later, Firefox ESR 115.5.0 or later, or Thunderbird 115.5 or later.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
FirefoxWeb browser
Affected:< 120.0
Firefox EsrWeb browser
Affected:< 115.5.0
Debian LinuxOperating system
Affected:= 10.0= 11.0= 12.0
ThunderbirdApplication
Affected:< 115.5

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check Mozilla Firefox version
    Open Firefox and navigate to about:support, or run 'firefox --version' from command line
    Affected if Version is earlier than 120.0
  2. Check Mozilla Firefox ESR version
    Open Firefox ESR and navigate to about:support, or run 'firefox-esr --version' from command line
    Affected if Version is earlier than 115.5.0
  3. Check Mozilla Thunderbird version
    Open Thunderbird and navigate to About Thunderbird, or run 'thunderbird --version' from command line
    Affected if Version is earlier than 115.5
  4. Check Debian Linux version (if running Mozilla packages from Debian repos)
    Run 'cat /etc/debian_version' or 'lsb_release -a'
    Affected if Version is 10.0, 11.0, or 12.0 and Mozilla packages from Debian repositories are installed

You are affected if you run any Firefox version below 120.0, Firefox ESR below 115.5.0, or Thunderbird below 115.5, or if you run Mozilla packages from Debian 10, 11, or 12.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 115.5 / 115.5.0 / 120.0 or later
Fixed in 115.5115.5.0120.0
Interim mitigation

Update to the fixed versions: Firefox 120 or later, Firefox ESR 115.5.0 or later, or Thunderbird 115.5 or later.

Recommended fix High confidence

Firefox 120.0, Firefox ESR 115.5.0, Thunderbird 115.5

  1. Verify current browser version by navigating to about:support in Firefox or Thunderbird
  2. Download the appropriate fixed release for your operating system from the official Mozilla website (www.mozilla.org)
  3. For Firefox: Upgrade to version 120.0 or later
  4. For Firefox ESR: Upgrade to version 115.5.0 or later
  5. For Thunderbird: Upgrade to version 115.5 or later
  6. Alternatively, use your system's package manager to update (e.g., apt update && apt upgrade for Debian-based systems)
  7. Restart the browser application after upgrade completes
  8. Verify the update was successful by checking the version in about:support
Caveat Standard security update with no expected breaking changes; minor version upgrade should preserve user settings and preferences

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Firefox Scoped from the published advisory
  • Consultation1.0 h
  • Implementation1.0 h
  • Testing1.0 h
  • Review / QA1.0 h
4.0 hours of engineering $750
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,200.

Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2023-6209 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data