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FirefoxWeb browser · Mozilla

CVE-2016-5271

MEDIUM · 6.5 CVSS v3.0 Published 2016-09-22
Fix available
A fix is available. Upgrade to after 48.0.2 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
The PropertyProvider::GetSpacingInternal function in Mozilla Firefox before 49.0 allows remote attackers to cause a denial of service (out-of-bounds read and application crash) via text runs in conjunction with a "display: contents" Cascading Style Sheets (CSS) property.

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 Firefox before version 49.0 contains an out-of-bounds read vulnerability in PropertyProvider::GetSpacingInternal when processing text runs with the 'display: contents' CSS property, leading to denial of service via application crash.

MitigationUpgrade Firefox to version 49.0 or later, or apply the vendor patch, to address the out-of-bounds read in the GetSpacingInternal function.

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:<= 48.0.2

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
None
Integrity
None
Availability
High

CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/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
    Open Firefox, click the menu button (three horizontal lines), then Help > About Firefox. The version number will display in the window that opens.
    Affected if The version shown is 48.0.2 or earlier (any version up to and including 48.0.2)
  2. Identify use of display: contents CSS
    Search web application codebases and CSS files for the string 'display: contents' or the CSS rule 'display: contents' applied to any element.
    Affected if Any webpage loaded in the browser contains elements with 'display: contents' CSS property applied
  3. Verify text rendering context
    If display: contents is present, confirm it is applied to text-containing elements (such as paragraphs, spans, or heading tags) rather than only to container elements like divs.
    Affected if Text-rendering elements (p, span, h1-h6, etc.) have display: contents applied

A user is affected if they are running Firefox version 48.0.2 or earlier AND viewing or running web content that utilizes the 'display: contents' CSS property on text elements, as this specific combination triggers the out-of-bounds read in PropertyProvider::GetSpacingInternal.

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 a release after 48.0.2
Interim mitigation

Upgrade Firefox to version 49.0 or later, or apply the vendor patch, to address the out-of-bounds read in the GetSpacingInternal function.

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-2016-5271 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