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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
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
Which versions are affected by CVE-2026-59877?
4 open source packages ship an affected version, including protobufjs. It affects 1 product.
| Package | 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 include 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.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
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 protobufjs Prototype Pollution vulnerability
- CVE-2026-41242 protobufjs has an arbitrary code execution issue
- CVE-2022-25878 Prototype Pollution
- CVE-2026-44291 protobufjs: Code generation gadget after prototype pollution
- CVE-2026-44293 protobufjs: Code injection through bytes field defaults in generated toObject code
Sources
Also known as CLEANSTART-2026-PW61027, CLEANSTART-2026-SF05781, CLSA-2026-1792476163, ECHO-9438-ca8d-8130, GHSA-j3f2-48v5-ccww, MINI-6x8j-4p58-28f4 and 10 more.