5.3

CVSS Score

3.1

-

CVSS Score

Basic Information

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CVE-2026-31808

CVE-2026-31808: file-type affected by infinite loop in ASF parser on malformed input with zero-size sub-header

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.

(GitHub Advisory)

Miggo Vulnerability Database

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CVE-2026-31808

CVE-2026-31808:

5.3

CVSS Score

3.1

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
file-type	npm	>= 13.0.0, < 21.3.1	21.3.1

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability lies in the ASF file parsing logic within the file-type library. The provided commit patch clearly shows modifications to the core.js file, specifically within a loop that processes ASF file headers. The vulnerability description explains that a zero-size sub-header leads to a negative payload calculation, causing tokenizer.ignore() to move the stream position backward, resulting in an infinite loop. The patch mitigates this by adding a check to ensure the stream position always advances, breaking the loop if it does not. The affected code is located within the parse method of the FileTypeParser class, as identified by analyzing the structure of core.js. The test case added in test.js confirms the fix by using fileTypeFromBuffer, which internally uses the FileTypeParser.

Vulnerable functions

FileTypeParser.parse

core.js

The `parse` function in the `FileTypeParser` class is vulnerable to an infinite loop. When parsing a crafted ASF file with a sub-header size of zero, the calculated `payload` becomes negative. This causes `tokenizer.ignore(payload)` to move the read position backward, leading to the same sub-header being processed repeatedly in an infinite loop, causing a denial of service.

Vulnerability Intelligence
Miggo AI

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WAF Rule

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Reasoning

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