CVE-2026-31808: file-type affected by infinite loop in ASF parser on malformed input with zero-size sub-header
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.
Patches Fixed in version 21.3.1. Users should upgrade to >= 21.3.1.
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
crnkovic@lokvica.com
Other sources
file-type detects the file type of a file, stream, or data. Prior to 21.3.1, 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. Fixed in version 21.3.1.
— MITRE
Affected Software
Remediation
Event History
Frequently Asked Questions
What is the severity of CVE-2026-31808?
CVE-2026-31808 has a severity rating of medium due to its potential to cause denial of service.
How do I fix CVE-2026-31808?
To fix CVE-2026-31808, upgrade the file-type package to version 21.3.1 or later.
What systems are affected by CVE-2026-31808?
CVE-2026-31808 affects versions of the file-type package prior to 21.3.1.
What type of vulnerability is CVE-2026-31808?
CVE-2026-31808 is a denial of service vulnerability caused by an infinite loop in the ASF parser.
What can happen if CVE-2026-31808 is exploited?
If exploited, CVE-2026-31808 can lead to an infinite loop that results in denial of service for applications using the affected file-type parser.