Summary
Workarounds
Is there a way for users to fix or remediate the vulnerability without upgrading?
There is no direct code-level workaround within the library itself. However, users can mitigate the risk by:
- Validating and sanitizing all input before passing it to the
serialize()function. - Ensuring the environment is protected against Prototype Pollution.
- Upgrading to
v7.0.5as soon as possible.
Acknowledgements
Serialize JavaScript thanks Tomer Aberbach (@TomerAberbach) for discovering and privately disclosing this issue.
Impact
What kind of vulnerability is it?
It is a Denial of Service (DoS) vulnerability caused by CPU exhaustion. When serializing a specially crafted "array-like" object (an object that inherits from Array.prototype but has a very large length property), the process enters an intensive loop that consumes 100% CPU and hangs indefinitely.
Who is impacted?
Applications that use serialize-javascript to serialize untrusted or user-controlled objects are at risk. While direct exploitation is difficult, it becomes a high-priority threat if the application is also vulnerable to Prototype Pollution or handles untrusted data via YAML Deserialization, as these could be used to inject the malicious object.
Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.
CVE-2026-34043 has a CVSS score of 5.9 (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 (7.0.5); 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
Has the problem been patched?
Yes, the issue has been patched by replacing instanceof Array checks with Array.isArray() and using Object.keys() for sparse array detection.
What versions should users upgrade to?
Users should upgrade to v7.0.5 or later.
Frequently Asked Questions
- What is CVE-2026-34043? CVE-2026-34043 is a medium-severity uncontrolled resource consumption vulnerability in serialize-javascript (npm), affecting versions >= 5.0.0, < 7.0.5. It is fixed in 7.0.5. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
- How severe is CVE-2026-34043? CVE-2026-34043 has a CVSS score of 5.9 (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 serialize-javascript are affected by CVE-2026-34043? serialize-javascript (npm) versions >= 5.0.0, < 7.0.5 is affected.
- Is there a fix for CVE-2026-34043? Yes. CVE-2026-34043 is fixed in 7.0.5. Upgrade to this version or later.
- Is CVE-2026-34043 exploitable, and should I be worried? Whether CVE-2026-34043 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-2026-34043 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-2026-34043? Upgrade
serialize-javascriptto 7.0.5 or later.