CVE-2026-42040 Axios: Null Byte Injection via Reverse-Encoding in AxiosURLSearchParams
Axios library incorrectly decodes null bytes in URL parameters, potentially allowing null byte injection in specific non-standard usage scenarios.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-42040?
CVE-2026-42040 is a low-severity vulnerability in axios, published on 24 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-42040?
4 open source packages ship an affected version, including axios. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
axios npm | All versions | 0.31.1 |
axios npm | All versions | 0.31.1 |
axios npm | From 1.0.0 | 1.15.1 |
axios npm | From 1.0.0 | 1.15.1 |
Products include Axios Axios.
How do I fix CVE-2026-42040?
Upgrade axios to a fixed version for your release line: 0.31.1 or 1.15.1.
Is CVE-2026-42040 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-42040 exists.
Other vulnerabilities in axios
- CVE-2026-44494 Axios: Full Man-in-the-Middle via Prototype Pollution Gadget in `config.proxy`
- CVE-2026-44492 axios's shouldBypassProxy does not recognize IPv4-mapped IPv6 addresses, allowing NO_PROXY bypass (incomplete fix for CVE-2025-62718)
- CVE-2026-67320 axios before 0.33.0 Prototype Pollution via Node HTTP adapter
- CVE-2026-44487 Axios: Proxy-Authorization Credential Leak to Origin Server Across HTTP-to-HTTPS Redirect in Axios Node.js HTTP Adapter
- CVE-2025-27152 Possible SSRF and Credential Leakage via Absolute URL in axios Requests
Sources
Also known as CLEANSTART-2026-CE61483, CLEANSTART-2026-LV58497, DEBIAN-CVE-2026-42040, ECHO-765e-d879-a5bc, GHSA-xhjh-pmcv-23jw, MINI-2344-jr23-jcqx and 20 more.