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FirefoxWeb browser · Mozilla

CVE-2009-0777

MEDIUM · 5.8 CVSS v2.0 Published 2009-03-05
Fix available
A fix is available. Upgrade to after 3.0.6 or later.
See remediation →
67/100
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
Mozilla Firefox before 3.0.7, Thunderbird before 2.0.0.21, and SeaMonkey before 1.1.15 decode invisible characters when they are displayed in the location bar, which causes an incorrect address to be displayed and makes it easier for remote attackers to spoof URLs and conduct phishing attacks.

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, Thunderbird, and SeaMonkey contained a vulnerability where invisible Unicode characters in URLs were decoded and displayed in the location bar, causing the displayed address to differ from the actual URL being visited. This allowed remote attackers to spoof URLs and conduct phishing attacks by tricking users into believing they were on a legitimate site.

MitigationUpgrade to Firefox 3.0.7 or later, Thunderbird 2.0.0.21 or later, or SeaMonkey 1.1.15 or later to resolve this vulnerability.

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:<= 3.0.6= 1.0= 1.0.1= 1.0.2= 1.0.3= 1.0.4= 1.0.5= 1.0.6= 1.0.7= 1.0.8= 1.5= 1.5.0.1
SeamonkeyApplication
Affected:<= 1.1.14= 1.0= 1.0.1= 1.0.2= 1.0.3= 1.0.5= 1.0.6= 1.0.7= 1.0.8= 1.0.9= 1.1= 1.1.1
ThunderbirdApplication
Affected:<= 2.0.0.20= 2.0.0.0= 2.0.0.4= 2.0.0.5= 2.0.0.6= 2.0.0.9= 2.0.0.12= 2.0.0.14= 2.0.0.16= 2.0.0.17= 2.0.0.18= 2.0.0.19

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
M
Authentication
None
Confidentiality
None
Integrity
Partial
Availability
Partial

AV:N/AC:M/Au:N/C:N/I:P/A:P

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. Identify installed Firefox version
    Run 'firefox --version' from command line, or open Firefox and go to Help > About Firefox to view the version number
    Affected if Version is 3.0.6 or earlier, or is one of the listed 1.x versions (1.0 through 1.0.8, 1.5.0.1)
  2. Identify installed SeaMonkey version
    Run 'seamonkey --version' from command line, or open SeaMonkey and go to Help > About SeaMonkey to view the version number
    Affected if Version is 1.1.14 or earlier, or is one of the listed 1.x versions (1.0 through 1.1.1)
  3. Identify installed Thunderbird version
    Run 'thunderbird --version' from command line, or open Thunderbird and go to Help > About Thunderbird to view the version number
    Affected if Version is 2.0.0.20 or earlier, or is one of the listed 2.0.0.x versions (2.0.0.0, 2.0.0.4-2.0.0.19)

If any of these Mozilla products are installed and the detected version matches the affected ranges listed (Firefox <= 3.0.6 or specific 1.x versions, SeaMonkey <= 1.1.14 or specific 1.x versions, Thunderbird <= 2.0.0.20 or specific 2.x versions), the environment is vulnerable to URL spoofing via invisible Unicode characters.

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 3.0.6
Interim mitigation

Upgrade to Firefox 3.0.7 or later, Thunderbird 2.0.0.21 or later, or SeaMonkey 1.1.15 or later to resolve this vulnerability.

Fix this in Firefox Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing1.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,090
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,744.

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-2009-0777 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