# CVE-2019-3556: Path traversal in HHVM

> An attacker with access to the HHVM admin server can overwrite arbitrary files via an unvalidated path parameter in the dump-pcre-cache handler.

- **Severity:** High 8.1 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 26 Oct 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-36h6-q98c-7j6j, UBUNTU-CVE-2019-3556

## What is CVE-2019-3556?

CVE-2019-3556 is a high-severity path traversal vulnerability in Facebook HHVM, published on 26 Oct 2021. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

HHVM supports the use of an "admin" server which accepts administrative requests over HTTP. One of those request handlers, dump-pcre-cache, can be used to output cached regular expressions from the current execution context into a file. The handler takes a parameter which specifies where on the filesystem to write this data. The parameter is not validated, allowing a malicious user to overwrite arbitrary files where the user running HHVM has write access. This issue affects HHVM versions prior to 4.56.2, all versions between 4.57.0 and 4.78.0, as well as 4.79.0, 4.80.0, 4.81.0, 4.82.0, and 4.83.0.

Weakness: CWE-22 (Improper Limitation of a Pathname to a Restricted Directory)

## Which versions are affected by CVE-2019-3556?

It affects 1 product.


Products: Facebook Hhvm.

## How do I fix CVE-2019-3556?

No fix has been published for CVE-2019-3556 yet. Limit exposure of the affected software until one is available.

## Is CVE-2019-3556 being exploited?

There is no known exploitation of CVE-2019-3556 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-2019-3556 and fix it if it is affected.

What it is: CVE-2019-3556 is a high-severity path traversal vulnerability in Facebook HHVM, published on 26 Oct 2021. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2019-3556 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-2019-3556/ (Markdown: https://insights.sbomify.com/CVE-2019-3556/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2019-3556
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2019-3556
- OSV: https://osv.dev/vulnerability/CVE-2019-3556

---
From sbomify Insights: https://insights.sbomify.com/CVE-2019-3556/
Summaries are generated and may contain mistakes; the official description above is the record.