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FirefoxWeb browser · Mozilla

CVE-2023-6208

HIGH · 8.8 CVSS v3.1 Published 2023-11-21
Fix available
A fix is available. Upgrade to 115.5 / 115.5.0 or later.
See remediation →
95/100
Remediation priority · Urgent
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
When using X11, text selected by the page using the Selection API was erroneously copied into the primary selection, a temporary storage not unlike the clipboard. *This bug only affects Firefox on X11. Other systems are unaffected.* 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

On X11 systems, the Selection API erroneously copies text selected on webpages to the X11 primary selection (temporary storage accessible via middle-click), allowing potentially sensitive page content to become accessible system-wide to other applications without explicit user action.

MitigationUpdate affected applications to Firefox 120+, Firefox ESR 115.5.0+, or Thunderbird 115.5+ to patch the vulnerability.

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
High
Availability
High

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

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 if the system uses X11 display server
    Run 'echo $XDG_SESSION_TYPE' or 'loginctl show-session $(loginctl | grep seat | awk "{print $1}") -p Type' to determine the display server type. The vulnerability only applies on X11, not Wayland.
    Affected if The session type is X11 rather than Wayland or other display servers.
  2. Determine installed Firefox version
    Run 'firefox --version' or check 'Help > About Firefox' in the application menu. Record the full version number (e.g., 119.0.1).
    Affected if The installed Firefox version is below 120.0 (for regular Firefox) or below 115.5.0 (for Firefox ESR).
  3. Determine installed Thunderbird version
    Run 'thunderbird --version' or check 'Help > About Thunderbird' in the application menu. Record the full version number.
    Affected if Thunderbird is installed and its version is below 115.5.0.
  4. Verify Debian package version if using system packages
    On Debian-based systems, run 'dpkg -l | grep -E "(firefox|thunderbird)"' to check installed package versions. Compare against Debian 10, 11, or 12 which ship vulnerable Firefox versions.
    Affected if The system is Debian 10, 11, or 12 with Firefox packages from the default repositories.

A user is affected if they run Firefox below 120.0 (or ESR below 115.5.0), or Thunderbird below 115.5.0, on an X11 display server.

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 affected applications to Firefox 120+, Firefox ESR 115.5.0+, or Thunderbird 115.5+ to patch the vulnerability.

Recommended fix High confidence

Firefox 120.0, Firefox ESR 115.5.0, or Thunderbird 115.5

  1. Check current Firefox/Thunderbird version by navigating to about:support or running 'firefox --version' / 'thunderbird --version'
  2. Update your system package manager: 'sudo apt update' (Debian/Ubuntu) or equivalent for your distribution
  3. Upgrade the affected package: 'sudo apt upgrade firefox' or 'sudo apt upgrade thunderbird' for Debian-based systems
  4. For manual update, download Firefox 120.0 or later from www.mozilla.org, or Firefox ESR 115.5.0 or later
  5. For Thunderbird, download version 115.5 or later from www.mozilla.org
  6. After installation, restart the browser/mail client to apply the update
  7. Verify the fix by checking 'about:support' to confirm you are running version 120.0+ (Firefox), 115.5.0+ (Firefox ESR), or 115.5+ (Thunderbird)

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

Fix this in Firefox Scoped from the published advisory
  • Consultation1.0 h
  • Implementation2.0 h
  • Testing1.0 h
  • Review / QA1.0 h
5.0 hours of engineering $890
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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-2023-6208 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