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.