Critical · published July 3, 2026
When reusing a libcurl handle for sequential transfers driven by
environment-variable proxy configuration, libcurl fails to clear the proxy
authentication state between requests. Specifically, if the initial transfer
authenticates against `proxyA` using Digest auth, a subsequent transfer routed
through `proxyB` erroneously leaks the `Proxy-Authorization:` header intended
solely for `proxyA`.
| Product | Versions | Fixed in |
|---|---|---|
| haxx/curl | ≥ 7.12.0, < 8.21.0 | 8.21.0 |