# CVE-2020-1921: Memory corruption in HHVM

> A buffer overflow in HHVM's crypt function allows attackers to execute arbitrary code or cause a denial of service via crafted input.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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:** 10 Mar 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-x3g2-p3p4-fghf, UBUNTU-CVE-2020-1921

## What is CVE-2020-1921?

CVE-2020-1921 is a high-severity memory corruption vulnerability in Facebook HHVM, published on 10 Mar 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the crypt function, we attempt to null terminate a buffer using the size of the input salt without validating that the offset is within the buffer. This issue affects HHVM versions prior to 4.56.3, all versions between 4.57.0 and 4.80.1, all versions between 4.81.0 and 4.93.1, and versions 4.94.0, 4.95.0, 4.96.0, 4.97.0, 4.98.0.

Weakness: CWE-787 (Out-of-bounds Write), CWE-121 (Stack-based Buffer Overflow)

## Which versions are affected by CVE-2020-1921?

It affects 1 product.


Products: Facebook Hhvm.

## How do I fix CVE-2020-1921?

No fix has been published for CVE-2020-1921 yet. Limit exposure of the affected software until one is available.

## Is CVE-2020-1921 being exploited?

There is no known exploitation of CVE-2020-1921 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-2020-1900](https://insights.sbomify.com/CVE-2020-1900/): Use after free in HHVM (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)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-1921 and fix it if it is affected.

What it is: CVE-2020-1921 is a high-severity memory corruption vulnerability in Facebook HHVM, published on 10 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-2020-1921 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-2020-1921/ (Markdown: https://insights.sbomify.com/CVE-2020-1921/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-1921
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-1921
- OSV: https://osv.dev/vulnerability/CVE-2020-1921

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-1921/
Summaries are generated and may contain mistakes; the official description above is the record.