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FirefoxWeb browser · Mozilla

CVE-2019-17023

MEDIUM · 6.5 CVSS v3.1 Published 2020-01-08
Fix available
A fix is available. Upgrade to 72.0 or later.
See remediation →
72/100
Remediation priority · Elevated
Remotely reachable No privileges

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
After a HelloRetryRequest has been sent, the client may negotiate a lower protocol that TLS 1.3, resulting in an invalid state transition in the TLS State Machine. If the client gets into this state, incoming Application Data records will be ignored. This vulnerability affects Firefox < 72.

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

TLS 1.3 state machine logic flaw in Firefox where after a HelloRetryRequest, the client can incorrectly negotiate a lower TLS protocol version, causing an invalid state transition that causes incoming Application Data records to be ignored, resulting in a denial of service condition.

MitigationUpgrade Firefox to version 72 or later to obtain the fixed TLS state machine implementation.

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:< 72.0
Ubuntu LinuxOperating system
Affected:= 16.04= 18.04= 19.04= 19.10= 20.04
Debian LinuxOperating system
Affected:= 10.0

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
Required
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/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 checks

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

  1. Check if Firefox is installed
    On Linux: which firefox or dpkg -l | grep firefox. On Windows: check Program Files for Mozilla Firefox folder. On macOS: check /Applications for Firefox.app
    Affected if Firefox is present on the system
  2. Determine installed Firefox version
    Run 'firefox --version' from command line, or open Firefox and navigate to Help > About Firefox
    Affected if Version returned is blank or shows a version number
  3. Compare against vulnerable version range
    Compare the installed version number to the affected range: any version less than 72.0 is vulnerable (e.g., 71.x, 70.x, 60.x, etc.)
    Affected if Installed version is less than 72.0 (for example, 71.0, 60.11, etc.)

The user is affected if Firefox is installed and its version is below 72.0, as this version range contains the vulnerable TLS 1.3 state machine logic.

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 72.0 or later
Fixed in 72.0
Interim mitigation

Upgrade Firefox to version 72 or later to obtain the fixed TLS state machine implementation.

Fix this in Firefox Scoped from the published advisory
  • Consultation1.0 h
  • Implementation1.0 h
  • Testing1.0 h
  • Review / QA1.0 h
4.0 hours of engineering $750
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,200.

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-2019-17023 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