# CVE-2018-6337: Weak cryptography in HHVM

> Forked processes reuse random buffers, causing predictable random numbers and weakening cryptographic security in applications using the folly library.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 31 Dec 2018
- **Updated:** 6 May 2025
- **Also known as:** GHSA-46jm-3g2r-j53x

## What is CVE-2018-6337?

CVE-2018-6337 is a high-severity vulnerability in Facebook HHVM, published on 31 Dec 2018. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

folly::secureRandom will re-use a buffer between parent and child processes when fork() is called. That will result in multiple forked children producing repeat (or similar) results. This affects HHVM 3.26 prior to 3.26.3 and the folly library between v2017.12.11.00 and v2018.08.09.00.

Weakness: CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer), CWE-212 (Improper Removal of Sensitive Information Before Storage or Transfer)

## Which versions are affected by CVE-2018-6337?

It affects 2 products.


Products: Facebook Folly, Facebook Hhvm.

## How do I fix CVE-2018-6337?

No fix has been published for CVE-2018-6337 yet. Limit exposure of the affected software until one is available.

## Is CVE-2018-6337 being exploited?

There is no known exploitation of CVE-2018-6337 in the wild and no public exploit code.

## Other vulnerabilities in Facebook HHVM

- [CVE-2021-24036](https://insights.sbomify.com/CVE-2021-24036/): Integer overflow in HHVM (critical 9.8)
- [CVE-2019-11934](https://insights.sbomify.com/CVE-2019-11934/): Memory corruption in folly (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2018-6337 and fix it if it is affected.

What it is: CVE-2018-6337 is a high-severity vulnerability in Facebook HHVM, published on 31 Dec 2018. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2018-6337 in the wild and no public exploit code.

Affected product: Facebook HHVM. 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-2018-6337/ (Markdown: https://insights.sbomify.com/CVE-2018-6337/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2018-6337
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2018-6337
- OSV: https://osv.dev/vulnerability/CVE-2018-6337

---
From sbomify Insights: https://insights.sbomify.com/CVE-2018-6337/
Summaries are generated and may contain mistakes; the official description above is the record.