# CVE-2026-59877: protobufjs: Denial of Service via infinite loop in .proto option parsing

> An attacker can cause a denial of service via an infinite loop in protobufjs by providing a crafted .proto schema that triggers premature termination during option parsing.

- **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:** 8 Jul 2026
- **Updated:** 8 Jul 2026
- **Also known as:** CLEANSTART-2026-PW61027, CLEANSTART-2026-SF05781, CLSA-2026-1792476163, ECHO-9438-ca8d-8130, GHSA-j3f2-48v5-ccww, MINI-6x8j-4p58-28f4, MINI-8547-9cp5-2x8f, MINI-9fc8-hm7w-9rwf, MINI-9q4f-fmcj-4vvf, MINI-fmmr-mfmc-5r85, MINI-frq7-69vq-r7h6, MINI-hx28-f59m-q9c8, MINI-hx65-h47g-wrq5, MINI-jgj4-q24r-993f, MINI-m72j-cv75-8cvp, ROOT-APP-NPM-CVE-2026-59877

## What is CVE-2026-59877?

CVE-2026-59877 is a medium-severity denial of service vulnerability in protobufjs protobuf.js, published on 8 Jul 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. Prior to 7.6.5 and 8.6.6, protobufjs parsed option names by advancing through schema tokens until reaching an = token without checking for end of input, so a crafted .proto schema that opens an option declaration and ends prematurely can cause parse, Root.load, or Root.loadSync to loop indefinitely. This issue is fixed in versions 7.6.5 and 8.6.6.

Weakness: CWE-835 (Loop with Unreachable Exit Condition)

## Which versions are affected by CVE-2026-59877?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `protobufjs` | npm | From 7.5.0 | 7.6.5 |
| `protobufjs` | npm | From 7.5.0 | 7.6.5 |
| `protobufjs` | npm | From 8.0.0 | 8.6.6 |
| `protobufjs` | npm | From 8.0.0 | 8.6.6 |

Products: Protobufjs Project Protobufjs.

## How do I fix CVE-2026-59877?

Upgrade protobufjs to a fixed version for your release line: 7.6.5 or 8.6.6.

## Is CVE-2026-59877 being exploited?

There is no known exploitation of CVE-2026-59877 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-2026-59877 and fix it if it is affected.

What it is: CVE-2026-59877 is a medium-severity denial of service vulnerability in protobufjs protobuf.js, published on 8 Jul 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-2026-59877 in the wild and no public exploit code.

Affected packages and fixed versions:
- protobufjs (npm): affected from 7.5.0; fixed in 7.6.5
- protobufjs (npm): affected from 7.5.0; fixed in 7.6.5
- protobufjs (npm): affected from 8.0.0; fixed in 8.6.6
- protobufjs (npm): affected from 8.0.0; fixed in 8.6.6

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-2026-59877/ (Markdown: https://insights.sbomify.com/CVE-2026-59877/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-59877
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-59877
- OSV: https://osv.dev/vulnerability/CVE-2026-59877

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-59877/
Summaries are generated and may contain mistakes; the official description above is the record.