# CVE-2026-59877: protobufjs infinite loop in .proto option parsing

Source: https://junglewise.ai/threats/cve-2026-59877-protobufjs-infinite-loop-in-proto-option-parsing  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-08. Updated: 2026-07-20  
License: CC BY 4.0 with a link back

CVE-2026-59877 · Severity: medium · CVSS 5.3 · Published 2026-07-08

A vulnerability in the protobufjs library can allow an attacker to crash or freeze a Node.js application. By providing a specially crafted schema file, an attacker can trigger an infinite loop during the parsing process. Because Node.js handles tasks one at a time, this loop blocks all other operations, leading to a complete service outage until the application is manually restarted.

Technologies: [protobufjs (npm)](https://junglewise.ai/threats/technologies/protobufjs). Vendors: [npm](https://junglewise.ai/threats/vendors/npm).

## Quick answers

**Is CVE-2026-59877 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-59877 being exploited in the wild.

**How severe is CVE-2026-59877?** Medium severity, with a CVSS score of 5.3, published 8 July 2026.

**Which products and versions are affected?** protobufjs (npm) SEMVER:introduced=7.5.0,fixed=7.6.5.

**Is there a fix for CVE-2026-59877?** Yes. protobufjs (npm): upgrade to 7.6.5 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-59877 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-59877?** Check whether you run protobufjs (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- protobufjs (npm): upgrade to 7.6.5 or later

  ```sh
  npm install protobufjs@7.6.5
  ```


## Technical details

An infinite loop vulnerability exists in protobufjs (CWE-835) within the reflection parsing path, specifically affecting the 'parse', 'Root.load', and 'Root.loadSync' methods. The root cause is the option parser's failure to check for the end of input while searching for an assignment operator ('=') in a .proto schema. An attacker can exploit this by providing a crafted schema that initiates an option declaration but terminates prematurely. In single-threaded Node.js environments, this results in a blocked event loop and a persistent Denial of Service. The issue is resolved in versions 7.6.5 and 8.6.6.

## Affected products

- protobufjs protobufjs >= 7.5.0, <= 7.6.4
- protobufjs protobufjs >= 8.0.0, <= 8.6.5

## Identifiers

- CVE-2026-59877
- GHSA-j3f2-48v5-ccww

## Timeline

- 2026-07-04: disclosed: Vulnerability reported to the maintainer
- 2026-07-08: advisory: NVD publication date
- 2026-07-20: advisory: GitHub Advisory published

## References

- [https://api.github.com/users/bilerden](https://api.github.com/users/bilerden)
- [https://github.com/bilerden](https://github.com/bilerden)
- [https://api.github.com/users/bilerden/gists%7B/gist_id%7D](https://api.github.com/users/bilerden/gists%7B/gist_id%7D)
- [https://api.github.com/users/bilerden/repos](https://api.github.com/users/bilerden/repos)
- [https://avatars.githubusercontent.com/u/32697241?v=4](https://avatars.githubusercontent.com/u/32697241?v=4)
- [https://api.github.com/users/bilerden/events%7B/privacy%7D](https://api.github.com/users/bilerden/events%7B/privacy%7D)

## Related threats

- [protobufjs prototype mutation in Text Format string map parsing](https://junglewise.ai/threats/cve-2026-59876-protobufjs-prototype-pollution-in-text-format-extension)
- [protobufjs memory amplification via unknown field preservation](https://junglewise.ai/threats/cve-2026-54270-protobufjs-memory-amplification-via-unknown-field-preservation)
- [protobufjs property shadowing and uncontrolled recursion](https://junglewise.ai/threats/cve-2026-54269-protobufjs-property-shadowing-and-uncontrolled-recursion)
- [protobufjs uncontrolled recursion in JSON conversion](https://junglewise.ai/threats/cve-2026-48712-protobufjs-uncontrolled-recursion-in-json-conversion)
- [protobufjs uncontrolled recursion in JSON descriptor expansion](https://junglewise.ai/threats/cve-2026-45740-protobufjs-uncontrolled-recursion-in-json-descriptor-expansion)