Summary
Workarounds
Validate or limit the size of input buffers before passing them to file-type, or run file type detection in a worker thread with a timeout.
References
- Fix commit: 319abf871b50ba2fa221b4a7050059f1ae096f4f
Reporter
Impact
A denial of service vulnerability exists in the ASF (WMV/WMA) file type detection parser. When parsing a crafted input where an ASF sub-header has a size field of zero, the parser enters an infinite loop. The payload value becomes negative (-24), causing tokenizer.ignore(payload) to move the read position backwards, so the same sub-header is read repeatedly forever.
Any application that uses file-type to detect the type of untrusted/attacker-controlled input is affected. An attacker can stall the Node.js event loop with a 55-byte payload.
CVE-2026-31808 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 (21.3.1); 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
Fixed in version 21.3.1. Users should upgrade to >= 21.3.1.
Frequently Asked Questions
- What is CVE-2026-31808? CVE-2026-31808 is a medium-severity security vulnerability in file-type (npm), affecting versions >= 13.0.0, < 21.3.1. It is fixed in 21.3.1.
- How severe is CVE-2026-31808? CVE-2026-31808 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 file-type are affected by CVE-2026-31808? file-type (npm) versions >= 13.0.0, < 21.3.1 is affected.
- Is there a fix for CVE-2026-31808? Yes. CVE-2026-31808 is fixed in 21.3.1. Upgrade to this version or later.
- Is CVE-2026-31808 exploitable, and should I be worried? Whether CVE-2026-31808 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-2026-31808 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-2026-31808? Upgrade
file-typeto 21.3.1 or later.