FirefoxWeb browser · Mozilla
CVE-2016-5254
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 · uneditedUse-after-free vulnerability in the nsXULPopupManager::KeyDown function in Mozilla Firefox before 48.0 and Firefox ESR 45.x before 45.3 allows attackers to execute arbitrary code or cause a denial of service (heap memory corruption and application crash) by leveraging keyboard access to use the Alt key during selection of top-level menu items.
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 confidenceUse-after-free vulnerability in Mozilla Firefox's nsXULPopupManager::KeyDown function. When the Alt key is pressed during selection of top-level menu items, the application accesses freed heap memory, causing corruption that can lead to arbitrary code execution or denial of service.
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
<= 47.0.1= 45.1.0= 45.1.1= 45.2.0= 45.3.0
LinuxOperating system
= 5.0= 6= 7CVSS 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
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/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 checksWork through these to decide whether this CVE applies to you.
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Verify Firefox is installedOn Linux: run 'which firefox' or 'rpm -qa | grep -i firefox'. On Windows: check if C:\Program Files\Mozilla Firefox exists. On macOS: check if /Applications/Firefox.app existsAffected if Firefox is not present on the system
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Determine Firefox versionOn Linux: run 'firefox --version'. On Windows: run 'firefox.exe -v' from the Firefox directory or type 'about:firefox' in address bar. On macOS: right-click Firefox.app, select Get InfoAffected if Version cannot be determined or Firefox not found
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Compare version to affected rangesCompare the installed version against: 45.1.0, 45.1.1, 45.2.0, 45.3.0, or any version <= 47.0.1. Note that versions 45.0.x are also affected since 45.3.0 was the fixed ESR versionAffected if Installed version is exactly 45.1.0, 45.1.1, 45.2.0, or 45.3.0; or is 47.0.1 or lower; or is any 45.0.x version
User is affected if Firefox is installed and the version is 45.1.0, 45.1.1, 45.2.0, 45.3.0, any 45.0.x, or any version 47.0.1 or lower
Generated from the published advisory. Verify against your own configuration.
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 · scopedUpdate Firefox to version 48.0 or later, or Firefox ESR to version 45.3 or later to patch the use-after-free vulnerability.
Firefox 48.0 or later (or Firefox ESR 45.3+ for ESR users)
- Check current Firefox version by navigating to Help > About Firefox
- If using Firefox stable version before 48.0: upgrade to Firefox 48.0 or later (preferably the latest stable release)
- If using Firefox ESR 45.x: upgrade to Firefox ESR 45.3 or later
- Restart Firefox after the upgrade
- Verify the new version is installed by checking Help > About Firefox again
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Firefox
Scoped from the published advisory
- Consultation2.0 h
- Implementation1.0 h
- Testing2.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,696.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2016-5254 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2016-5254 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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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.
- 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
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