FirefoxWeb browser · Mozilla
CVE-2017-7761
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 · uneditedThe Mozilla Maintenance Service "helper.exe" application creates a temporary directory writable by non-privileged users. When this is combined with creation of a junction (a form of symbolic link), protected files in the target directory of the junction can be deleted by the Mozilla Maintenance Service, which has privileged access. Note: This attack requires local system access and only affects Windows. Other operating systems are not affected. This vulnerability affects Firefox ESR < 52.2 and Firefox < 54.
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 confidenceThe Mozilla Maintenance Service helper.exe creates a temporary directory with weak permissions writable by non-privileged Windows users. Attackers with local system access can create a junction (symbolic link) pointing to protected system files; when the privileged Maintenance Service accesses the temp directory, it follows the junction and deletes target files.
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
< 52.2.0< 54.0CVSS 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
- Local
- Complexity
- Low
- Privileges
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- High
- Availability
- None
CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/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 checksWork through these to decide whether this CVE applies to you.
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Check installed Firefox versionOpen Firefox, go to Help > About Firefox, or run 'firefox -v' from command line, or check registry key HKEY_LOCAL_MACHINE\SOFTWARE\Mozilla\Mozilla Firefox\CurrentVersionAffected if Version is below 52.2.0 or below 54.0 (non-ESR versions)
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Locate the Mozilla Maintenance Service helper.exeSearch for helper.exe in typical Mozilla installation paths: C:\Program Files\Mozilla Maintenance Service\helper.exe or within the Firefox installation directory under the Maintenance folderAffected if helper.exe exists on the system (vulnerable version present)
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Check if Mozilla Maintenance Service is installedOpen Windows Services (services.msc) and look for 'Mozilla Maintenance Service', or check registry HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MozillaMaintenanceAffected if Service is installed and set to run (creates temp directory with weak permissions on execution)
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Identify temp directory created by helper.exeWhen Mozilla Maintenance Service runs, it creates a temp directory (typically under %TEMP% or %LOCALAPPDATA%\Temp). Monitor directory creation during updates or run procmon during Maintenance Service execution to identify the specific temp pathAffected if The temp directory is created with weak permissions allowing write access from non-privileged user accounts
User is affected if running Firefox version below 52.2.0 (ESR) or below 54.0 with Mozilla Maintenance Service installed, where non-privileged local users can write to temp directories created by helper.exe.
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.
From vendor data52.2.054.0
Upgrade to Firefox ESR 52.2+, Firefox 54+, or later versions to eliminate the vulnerable helper.exe. On Windows systems where immediate upgrade is impractical, restrict local user access to the system and monitor for unauthorized junction creation.
Fix this in Firefox
Scoped from the published advisory
- Consultation1.0 h
- Implementation1.0 h
- Testing2.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2017-7761 — 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-2017-7761 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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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
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