# CVE-2026-55388: piscina: Prototype Pollution Gadget → RCE via inherited options.filename

> Attackers can achieve remote code execution in piscina worker pools by polluting the prototype to inject malicious filenames, requiring an upgrade to patched versions.

- **Severity:** High 8.1 (`CVSS:3.1/AV:N/AC:H/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:** Yes
- **Published:** 22 Jun 2026
- **Updated:** 23 Jun 2026
- **Also known as:** CLSA-2026-1784943103, CLSA-2026-1792231948, CLSA-2026-1792232060, ECHO-56d0-8d0e-4fc0, GHSA-x9g3-xrwr-cwfg, MINI-ff39-9whx-5gjq, MINI-mc69-jf7x-rvqv, MINI-mqgp-3j83-cwj6, MINI-p57f-f5c7-j3jw, MINI-p7g2-jr52-c5xh, MINI-pgmw-3mr6-9455, MINI-r84c-9c85-fpxr, MINI-wrjg-485m-87r3, ROOT-APP-NPM-CVE-2026-55388

## What is CVE-2026-55388?

CVE-2026-55388 is a high-severity code injection vulnerability in piscinajs piscina, published on 22 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

piscina is a node.js worker pool implementation. Prior to 6.0.0-rc.2, 5.2.0, and 4.9.3, piscina's constructor and run() paths read the filename option via plain member access. Both reads fall through the prototype chain when the caller's options object doesn't have filename as an own property. When Object.prototype.filename is polluted upstream the inherited value flows to worker_threads.Worker import and the attacker's .mjs runs in the worker. This vulnerability is fixed in 6.0.0-rc.2, 5.2.0, and 4.9.3.

Weakness: CWE-94 (Improper Control of Generation of Code), CWE-1321 (Improperly Controlled Modification of Object Prototype Attributes)

## Which versions are affected by CVE-2026-55388?

6 open source packages ship an affected version, including piscina.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `piscina` | npm | All versions | 4.9.3 |
| `piscina` | npm | All versions | 4.9.3 |
| `piscina` | npm | From 5.0.0-alpha.0 | 5.2.0 |
| `piscina` | npm | From 5.0.0-alpha.0 | 5.2.0 |
| `piscina` | npm | From 6.0.0-rc.1 | 6.0.0-rc.2 |
| `piscina` | npm | From 6.0.0-rc.1 | 6.0.0-rc.2 |

## How do I fix CVE-2026-55388?

Upgrade piscina to a fixed version for your release line: 4.9.3, 5.2.0 or 6.0.0-rc.2.

## Is CVE-2026-55388 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55388 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-55388 and fix it if it is affected.

What it is: CVE-2026-55388 is a high-severity code injection vulnerability in piscinajs piscina, published on 22 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55388 exists.

Affected packages and fixed versions:
- piscina (npm): affected all versions; fixed in 4.9.3
- piscina (npm): affected all versions; fixed in 4.9.3
- piscina (npm): affected from 5.0.0-alpha.0; fixed in 5.2.0
- piscina (npm): affected from 5.0.0-alpha.0; fixed in 5.2.0
- piscina (npm): affected from 6.0.0-rc.1; fixed in 6.0.0-rc.2
- piscina (npm): affected from 6.0.0-rc.1; fixed in 6.0.0-rc.2

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-2026-55388/ (Markdown: https://insights.sbomify.com/CVE-2026-55388/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-55388
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-55388
- OSV: https://osv.dev/vulnerability/CVE-2026-55388

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-55388/
Summaries are generated and may contain mistakes; the official description above is the record.