# CVE-2020-1918: Information disclosure in HHVM

> Attackers can read memory prior to in-memory buffers via negative seeking in data URI file operations, potentially exposing sensitive data.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/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:** 10 Mar 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-w4h2-wcmm-4gwq, UBUNTU-CVE-2020-1918

## What is CVE-2020-1918?

CVE-2020-1918 is a high-severity 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-memory file operations (ie: using fopen on a data URI) did not properly restrict negative seeking, allowing for the reading of memory prior to the in-memory 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-125 (Out-of-bounds Read), CWE-127 (Buffer Under-read)

## Which versions are affected by CVE-2020-1918?

It affects 1 product.


Products: Facebook Hhvm.

## How do I fix CVE-2020-1918?

No fix has been published for CVE-2020-1918 yet. Limit exposure of the affected software until one is available.

## Is CVE-2020-1918 being exploited?

There is no known exploitation of CVE-2020-1918 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-2020-1918 and fix it if it is affected.

What it is: CVE-2020-1918 is a high-severity 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-2020-1918 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-2020-1918/ (Markdown: https://insights.sbomify.com/CVE-2020-1918/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-1918
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-1918
- OSV: https://osv.dev/vulnerability/CVE-2020-1918

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From sbomify Insights: https://insights.sbomify.com/CVE-2020-1918/
Summaries are generated and may contain mistakes; the official description above is the record.