FirefoxWeb browser · Mozilla
CVE-2020-15677
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 · uneditedBy exploiting an Open Redirect vulnerability on a website, an attacker could have spoofed the site displayed in the download file dialog to show the original site (the one suffering from the open redirect) rather than the site the file was actually downloaded from. This vulnerability affects Firefox < 81, Thunderbird < 78.3, and Firefox ESR < 78.3.
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 confidenceFirefox/Thunderbird displayed the origin site (with open redirect) in the download file dialog instead of the actual download source, allowing UI spoofing. An attacker could exploit this to make users believe they're downloading from a trusted site when the file originates elsewhere.
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
< 81.0
Firefox EsrWeb browser
< 78.3
Debian LinuxOperating system
= 9.0= 10.0< 78.3= 15.1= 15.2CVSS 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
- Changed
- Confidentiality
- Low
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/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 checksWork through these to decide whether this CVE applies to you.
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Check Firefox version on Windows or macOSOpen Firefox, click Help > About Firefox (or on macOS Firefox > About Firefox) and note the version number displayedAffected if Version is less than 81.0 (for example, 80.x or lower)
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Check Firefox version on LinuxOpen a terminal and run: firefox --versionAffected if Version is less than 81.0 (for example, 80.x or lower)
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Check Firefox ESR version on any platformOpen Firefox ESR, navigate to Help > About Mozilla Firefox and note the ESR designation and version numberAffected if Version is less than 78.3 (for example, 78.2 or lower)
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Check Thunderbird versionOpen Thunderbird, click Help > About Thunderbird and note the version number displayedAffected if Version is less than 78.3 (for example, 78.2 or lower)
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Query installed Firefox package on Debian/UbuntuRun: dpkg -l | grep -i firefox or apt-cache policy firefoxAffected if Package version shown is less than 81.0
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Query installed package on Red Hat/SUSE systemsRun: rpm -q firefox or rpm -q mozilla-firefoxAffected if Package version shown is less than 81.0
You are affected if you are running any version of Firefox below 81.0, Firefox ESR below 78.3, or Thunderbird below 78.3, as the download dialog in these versions can be tricked into displaying a misleading origin URL.
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 data78.381.0
Upgrade to Firefox >= 81, Thunderbird >= 78.3, or Firefox ESR >= 78.3 to resolve the dialog spoofing issue.
Fix this in Firefox
Scoped from the published advisory
- Consultation1.0 h
- Implementation1.0 h
- Testing1.0 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 $1,200.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2020-15677 — 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-2020-15677 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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