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FirefoxWeb browser · Mozilla

CVE-2019-11756

HIGH · 8.8 CVSS v3.1 Published 2020-01-08
Fix available
A fix is available. Upgrade to 71.0 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
Improper refcounting of soft token session objects could cause a use-after-free and crash (likely limited to a denial of service). This vulnerability affects Firefox < 71.

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

Memory management vulnerability in Firefox where improper reference counting of soft token session objects leads to a use-after-free condition. This can cause browser crashes and potentially enable arbitrary code execution if an attacker can manipulate heap memory layout, though the vendor rates this as primarily a denial-of-service issue.

MitigationUpgrade Firefox to version 71 or later to obtain the fixed version with proper reference counting implementation for session objects.

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:< 71.0

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. Determine installed Firefox version
    Navigate to Firefox menu > Help > About Firefox, or type 'about:support' in the address bar, or run 'firefox --version' from command line
    Affected if The displayed version number is lower than 71.0 (e.g., 70.0, 60.x, etc.)
  2. Confirm browser is the primary affected product
    Verify the software being checked is Mozilla Firefox and not a derived browser (like Firefox ESR, Thunderbird, or third-party browsers based on Firefox code)
    Affected if The affected product is Mozilla Firefox versions prior to 71.0
  3. Identify if session handling is in use
    The vulnerability involves soft token session objects - check if the browser has been used to handle authenticated web sessions or stored credentials
    Affected if The browser has been used for web sessions, though the vulnerability triggers during browser operation rather than requiring specific user configuration

The environment is affected if the installed Mozilla Firefox version is lower than 71.0.

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.

From vendor data
Upgrade available Upgrade to 71.0 or later
Fixed in 71.0
Interim mitigation

Upgrade Firefox to version 71 or later to obtain the fixed version with proper reference counting implementation for session objects.

Fix this in Firefox Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA1.0 h
10.0 hours of engineering $1,750
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,800.

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-2019-11756 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