What’s Vulnerable › Vulnerabilities

CVE-2019-17023

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2020-01-08 · updated 2026-06-17
• Weakness: CWE-287

Description

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.

Affected products

• Canonical Ubuntu Linux: 16.04, 18.04, 19.04, 19.10, 20.04
• Debian Linux: 10.0
• Mozilla Firefox: before 72.0 — fixed in 72.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 72.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1590001
• https://usn.ubuntu.com/4234-1/
• https://usn.ubuntu.com/4397-1/
• https://www.debian.org/security/2020/dsa-4726
• https://www.mozilla.org/security/advisories/mfsa2020-01/
• https://bugzilla.mozilla.org/show_bug.cgi?id=1590001
• https://usn.ubuntu.com/4234-1/
• https://usn.ubuntu.com/4397-1/
• https://www.debian.org/security/2020/dsa-4726
• https://www.mozilla.org/security/advisories/mfsa2020-01/

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