# CVE-2026-54270: protobufjs: Memory amplification from preserved unknown fields in binary decode

> Attackers can cause memory exhaustion and denial of service by sending crafted protobuf payloads with many unknown fields to applications using vulnerable protobufjs versions.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **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:** GHSA-94rc-8x27-4472, MINI-623v-wj9h-7mpw, ROOT-APP-NPM-CVE-2026-54270

## What is CVE-2026-54270?

CVE-2026-54270 is a medium-severity denial of service vulnerability in protobufjs protobuf.js, published on 22 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

protobufjs compiles protobuf definitions into JavaScript (JS) functions. From 8.2.0 to 8.4.2, protobufjs preserved unknown wire elements in message.$unknowns and did not provide a decode-time option to discard unknown fields before retaining them. A crafted protobuf payload containing many unknown fields could therefore cause a decoded message to retain substantially more memory than the input size would suggest, even when unknown-field round-tripping is not needed. protobufjs 8.5.0 added the relevant decode-time options, allowing applications that decode untrusted protobuf data to disable unknown-field retention during decode. protobufjs 8.6.2 flips the default so unknown fields are discarded unless explicitly opted into.

Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling)

## Which versions are affected by CVE-2026-54270?

2 open source packages ship an affected version, including protobufjs. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `protobufjs` | npm | From 8.2.0 | 8.5.0 |
| `protobufjs` | npm | From 8.2.0 | 8.5.0 |

Products: Protobufjs Project Protobufjs.

## How do I fix CVE-2026-54270?

Upgrade protobufjs to 8.5.0 or later.

## Is CVE-2026-54270 being exploited?

There is no known exploitation of CVE-2026-54270 in the wild and no public exploit code.

## Other vulnerabilities in protobufjs protobuf.js

- [CVE-2023-36665](https://insights.sbomify.com/CVE-2023-36665/): protobufjs Prototype Pollution vulnerability (critical 9.8)
- [CVE-2026-41242](https://insights.sbomify.com/CVE-2026-41242/): protobufjs has an arbitrary code execution issue (critical 9.4)
- [CVE-2022-25878](https://insights.sbomify.com/CVE-2022-25878/): Prototype Pollution (high 8.2)
- [CVE-2026-44291](https://insights.sbomify.com/CVE-2026-44291/): protobufjs: Code generation gadget after prototype pollution (high 8.1)
- [CVE-2026-44293](https://insights.sbomify.com/CVE-2026-44293/): protobufjs: Code injection through bytes field defaults in generated toObject code (high 7.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-54270 and fix it if it is affected.

What it is: CVE-2026-54270 is a medium-severity denial of service vulnerability in protobufjs protobuf.js, published on 22 Jun 2026. 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-2026-54270 in the wild and no public exploit code.

Affected packages and fixed versions:
- protobufjs (npm): affected from 8.2.0; fixed in 8.5.0
- protobufjs (npm): affected from 8.2.0; fixed in 8.5.0

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-2026-54270/ (Markdown: https://insights.sbomify.com/CVE-2026-54270/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-54270
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-54270
- OSV: https://osv.dev/vulnerability/CVE-2026-54270

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-54270/
Summaries are generated and may contain mistakes; the official description above is the record.