# CVE-2019-9791: Memory corruption in Firefox

> Type confusion in the IonMonkey JIT compiler allows arbitrary object reading and writing, potentially leading to code execution in Firefox and Thunderbird.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 26 Apr 2019
- **Updated:** 4 Aug 2024
- **Also known as:** DEBIAN-CVE-2019-9791, GHSA-9r58-49jg-hrq7, UBUNTU-CVE-2019-9791

## What is CVE-2019-9791?

CVE-2019-9791 is a critical memory corruption vulnerability in Mozilla Firefox, published on 26 Apr 2019. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

The type inference system allows the compilation of functions that can cause type confusions between arbitrary objects when compiled through the IonMonkey just-in-time (JIT) compiler and when the constructor function is entered through on-stack replacement (OSR). This allows for possible arbitrary reading and writing of objects during an exploitable crash. This vulnerability affects Thunderbird < 60.6, Firefox ESR < 60.6, and Firefox < 66.

Weakness: CWE-843 (Access of Resource Using Incompatible Type)

## Which versions are affected by CVE-2019-9791?

It affects 6 products.


Products: Mozilla Firefox, Mozilla Thunderbird, Redhat Enterprise Linux, Redhat Enterprise Linux Eus, Redhat Enterprise Linux Server Aus, Redhat Enterprise Linux Server Tus.

## How do I fix CVE-2019-9791?

Upgrade to a fixed version.

## Is CVE-2019-9791 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2019-9791 exists.

Public exploit code:

- Exploit chain for CVE-2019-9791 & CVE-2019-11708 against firefox 65.0 on windows 64bit (github_poc): https://github.com/Sp0pielar/CVE-2019-9791
- Spidermonkey - IonMonkey Type Inference is Incorrect for Constructors Entered via OSR (exploitdb)

## Other vulnerabilities in Mozilla Firefox

- [CVE-2019-11708](https://insights.sbomify.com/CVE-2019-11708/): Mozilla Firefox and Thunderbird Sandbox Escape (critical 10.0, exploited in the wild)
- [CVE-2010-3765](https://insights.sbomify.com/CVE-2010-3765/): Mozilla Multiple Products Remote Code Execution (critical 9.8, exploited in the wild)
- [CVE-2022-26486](https://insights.sbomify.com/CVE-2022-26486/): Mozilla Firefox Use-After-Free (critical 9.6, exploited in the wild)
- [CVE-2022-26485](https://insights.sbomify.com/CVE-2022-26485/): Mozilla Firefox Use-After-Free (high 8.8, exploited in the wild)
- [CVE-2019-11707](https://insights.sbomify.com/CVE-2019-11707/): Mozilla Firefox and Thunderbird Type Confusion (high 8.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2019-9791 and fix it if it is affected.

What it is: CVE-2019-9791 is a critical memory corruption vulnerability in Mozilla Firefox, published on 26 Apr 2019. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2019-9791 exists.

Affected product: Mozilla Firefox. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2019-9791/ (Markdown: https://insights.sbomify.com/CVE-2019-9791/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2019-9791
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2019-9791
- OSV: https://osv.dev/vulnerability/CVE-2019-9791

---
From sbomify Insights: https://insights.sbomify.com/CVE-2019-9791/
Summaries are generated and may contain mistakes; the official description above is the record.