CVE-2026-42040: Axios: Null Byte Injection via Reverse-Encoding in AxiosURLSearchParams

Severity: low (CVSS 3.7 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-04-24 · updated 2026-06-17
Weakness: CWE-116

Description

Axios is a promise based HTTP client for the browser and Node.js. Prior to 1.15.1 and 0.31.1, the encode() function in lib/helpers/AxiosURLSearchParams.js contains a character mapping (charMap) at line 21 that reverses the safe percent-encoding of null bytes. After encodeURIComponent('\x00') correctly produces the safe sequence %00, the charMap entry '%00': '\x00' converts it back to a raw null byte. Primary impact is limited because the standard axios request flow is not affected. This vulnerability is fixed in 1.15.1 and 0.31.1.

Affected products

axios: before 0.31.1; from 1.0.0 before 1.15.1 — fixed in 0.31.1, 1.15.1
Npm Axios: from 1.0.0 before 1.15.1; before 0.31.1 — fixed in 1.15.1, 0.31.1

How to fix

Upgrade to a fixed version: axios 0.31.1, 1.15.1; Npm Axios 1.15.1, 0.31.1. Check the vendor advisory for mitigations.

References

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