Summary
protobuf.js: Code generation gadget after prototype pollution
Full technical description
protobufjs used plain objects with inherited prototypes for internal type lookup tables used by generated encode and decode functions. If Object.prototype had already been polluted, those lookup tables could resolve attacker-controlled inherited properties as valid protobuf type information.
This could cause attacker-controlled strings to be emitted into generated JavaScript code.
Preconditions
- The application or one of its dependencies must allow an attacker to pollute
Object.prototype. - The polluted property must affect protobufjs internal type lookup behavior.
- The application must use protobufjs functionality that generates encode or decode code for affected types.
- The generated code path must be reached after the prototype pollution has occurred.
Workarounds
Avoid running affected versions in applications where attacker-controlled input can pollute Object.prototype. If immediate upgrade is not possible, remove or mitigate reachable prototype pollution primitives and isolate schema/message processing from untrusted application state.
Impact
An attacker who can first trigger a prototype pollution vulnerability may be able to influence generated protobufjs encode or decode functions in a way that can lead to arbitrary JavaScript execution.
This issue requires a separate prototype pollution primitive before protobufjs is invoked.
Applications without a reachable prototype pollution primitive are not directly exploitable through this issue alone.
Untrusted input is evaluated as executable code within the application's runtime environment. Typical impact: arbitrary code execution within the application's privilege context.
CVE-2026-44291 has a CVSS score of 8.1 (High). 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 (7.5.6, 8.0.2); 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.
Remediation advice
protobufjs to 7.5.6 or later; protobufjs to 8.0.2 or later
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-44291? CVE-2026-44291 is a high-severity code injection vulnerability in protobufjs (npm), affecting versions <= 7.5.5. It is fixed in 7.5.6, 8.0.2. Untrusted input is evaluated as executable code within the application's runtime environment.
- How severe is CVE-2026-44291? CVE-2026-44291 has a CVSS score of 8.1 (High). 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-2026-44291? protobufjs (npm) versions <= 7.5.5 is affected.
- Is there a fix for CVE-2026-44291? Yes. CVE-2026-44291 is fixed in 7.5.6, 8.0.2. Upgrade to this version or later.
- Is CVE-2026-44291 exploitable, and should I be worried? Whether CVE-2026-44291 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-2026-44291 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-2026-44291?
- Upgrade
protobufjsto 7.5.6 or later - Upgrade
protobufjsto 8.0.2 or later
- Upgrade