Summary
protobufjs: Denial of Service via infinite loop in .proto option parsing
protobufjs parsed option names by advancing through schema tokens until it reached an = token, without checking for end of input. A crafted .proto schema that opens an option declaration but ends prematurely could cause the option parser to loop without ever terminating.
This affects the reflection parsing path (parse, Root.load, Root.loadSync).
Preconditions
- The application must parse
.protoschema text influenced by an attacker. - The schema must be parsed through APIs such as
parse,Root.load, orRoot.loadSync. - The crafted input must begin an option declaration that ends before its
=assignment.
Workarounds
Do not parse .proto schemas from untrusted sources with affected versions. If untrusted schema text must be accepted, isolate parsing in a process or worker that can be safely terminated and bound it with a timeout, so a non-returning parse call cannot deny service to the rest of the application.
Impact
An attacker who can provide or influence .proto schema text parsed by an application may be able to cause the parsing call to never return. Because Node.js is single-threaded, the blocked event loop prevents all other work in the process, resulting in a denial of service that persists until the process is externally terminated.
Applications that only encode or decode protobuf binary data with trusted schemas are not directly affected.
CVE-2026-59877 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (7.6.5, 8.6.6); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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protobufjs to 7.6.5 or later; protobufjs to 8.6.6 or later
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-59877? CVE-2026-59877 is a medium-severity security vulnerability in protobufjs (npm), affecting versions >= 7.5.0, <= 7.6.4. It is fixed in 7.6.5, 8.6.6.
- How severe is CVE-2026-59877? CVE-2026-59877 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of protobufjs are affected by CVE-2026-59877? protobufjs (npm) versions >= 7.5.0, <= 7.6.4 is affected.
- Is there a fix for CVE-2026-59877? Yes. CVE-2026-59877 is fixed in 7.6.5, 8.6.6. Upgrade to this version or later.
- Is CVE-2026-59877 exploitable, and should I be worried? Whether CVE-2026-59877 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-59877 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-59877?
- Upgrade
protobufjsto 7.6.5 or later - Upgrade
protobufjsto 8.6.6 or later
- Upgrade