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FirefoxWeb browser · Mozilla

CVE-2017-7833

MEDIUM · 5.3 CVSS v3.0 Published 2018-06-11
Fix available
A fix is available. Upgrade to after 56.0.2 or later.
See remediation →
62/100
Remediation priority · Elevated
Remotely reachable No privileges Zero-click

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
Some Arabic and Indic vowel marker characters can be combined with Latin characters in a domain name to eclipse the non-Latin character with some font sets on the addressbar. The non-Latin character will not be visible to most viewers. This allows for domain spoofing attacks because these combined domain names do not display as punycode. This vulnerability affects Firefox < 57.

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

Firefox fails to properly render certain Arabic and Indic vowel marker characters when combined with Latin characters in domain names, causing the non-Latin portion to become invisible in the address bar due to font rendering issues. This allows attackers to create malicious domains that appear legitimate to users while bypassing punycode display protections.

MitigationUpgrade to Firefox 57 or later to receive the fix for proper IDN rendering and punycode display of internationalized domain names.

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:<= 56.0.2

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
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/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 checks

Work through these to decide whether this CVE applies to you.

  1. Check installed Firefox version
    Open Firefox, click the menu button, go to Help > About Firefox. The version number is displayed at the top.
    Affected if The version is 56.0.2 or lower (any version <= 56.0.2)
  2. Verify IDN support is enabled
    Type 'about:config' in the address bar, press Enter, then search for 'network.IDN'. Check if 'network.IDN.show_punycode' is set to false (the vulnerable configuration).
    Affected if network.IDN.show_punycode is false or missing, allowing IDN domains to display in their native script rather than punycode
  3. Check for IDN pref in config
    In about:config, search for 'network.IDN' to see all IDN-related preferences. Look for whether IDN display is fully enabled.
    Affected if IDN support is enabled without punycode display fallback, which allows the rendering vulnerability to be exploited

If Firefox version is 56.0.2 or lower AND IDN/punycode display is not forced to show punycode, the browser is vulnerable to invisible character rendering in internationalized domain names.

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 56.0.2
Interim mitigation

Upgrade to Firefox 57 or later to receive the fix for proper IDN rendering and punycode display of internationalized domain names.

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

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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-2017-7833 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