# CVE-2020-1900: Use after free in HHVM

> Attackers can trigger a use-after-free vulnerability in HHVM during object unserialization, potentially leading to code execution or denial of service.

- **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:** No
- **Published:** 11 Mar 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-g7r3-m2h7-28vw, UBUNTU-CVE-2020-1900

## What is CVE-2020-1900?

CVE-2020-1900 is a critical use after free vulnerability in Facebook HHVM, published on 11 Mar 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

When unserializing an object with dynamic properties HHVM needs to pre-reserve the full size of the dynamic property array before inserting anything into it. Otherwise the array might resize, invalidating previously stored references. This pre-reservation was not occurring in HHVM prior to v4.32.3, between versions 4.33.0 and 4.56.0, 4.57.0, 4.58.0, 4.58.1, 4.59.0, 4.60.0, 4.61.0, 4.62.0.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2020-1900?

It affects 1 product.


Products: Facebook Hhvm.

## How do I fix CVE-2020-1900?

No fix has been published for CVE-2020-1900 yet. Limit exposure of the affected software until one is available.

## Is CVE-2020-1900 being exploited?

There is no known exploitation of CVE-2020-1900 in the wild and no public exploit code.

## Other vulnerabilities in Facebook HHVM

- [CVE-2022-36937](https://insights.sbomify.com/CVE-2022-36937/): HHVM 4.172.0 and all prior versions use TLS 1.0 for secure connections when handling tls:// URLs in the stream extension. (critical 9.8)
- [CVE-2020-1916](https://insights.sbomify.com/CVE-2020-1916/): Integer overflow in HHVM (critical 9.8)
- [CVE-2020-1917](https://insights.sbomify.com/CVE-2020-1917/): Memory corruption in HHVM (critical 9.8)
- [CVE-2021-24025](https://insights.sbomify.com/CVE-2021-24025/): Integer overflow in HHVM (critical 9.8)
- [CVE-2016-1000004](https://insights.sbomify.com/CVE-2016-1000004/): Other in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-1900 and fix it if it is affected.

What it is: CVE-2020-1900 is a critical use after free vulnerability in Facebook HHVM, published on 11 Mar 2021. 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-2020-1900 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-2020-1900/ (Markdown: https://insights.sbomify.com/CVE-2020-1900/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-1900
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-1900
- OSV: https://osv.dev/vulnerability/CVE-2020-1900

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-1900/
Summaries are generated and may contain mistakes; the official description above is the record.