CVE-2026-42040: axios Improper Encoding

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.

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CVSS v3.1 Score

3.7

LOW

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS — Exploit Prediction

0.0006

Probability of exploitation

0.18%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-116 CWE-116

CWE-626 CWE-626

Affected Products

Vendor	Product	Versions
axios	axios	< 0.31.1
axios	axios	1.0.0 — 1.15.1

References

Advisories & Patches

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

Exploits

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

Frequently Asked Questions

What is CVE-2026-42040? +

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. It has a CVSS v3.1 base score of 3.7 (LOW).

How severe is CVE-2026-42040? +

CVE-2026-42040 has a CVSS v3.1 score of 3.7 out of 10, rated LOW. This is a low-severity vulnerability with limited impact. The EPSS score is 0.0006, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-42040? +

CVE-2026-42040 affects products from axios, specifically: axios. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-42040? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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