CVE-2026-5222

The Rust Security Response Team was notified that Cargo incorrectly normalized the URLs of third-party registries using the [sparse index protocol][1]. If a hosting provider allowed multiple registries to be hosted with arbitrary names within the same domain, an attacker able to publish crates in a registry could obtain the credentials of others users of the same registry. This vulnerability is tracked as CVE-2026-5222. The severity of the vulnerability is **low**, due to the extremely niche requirements needed to achieve the attack. ## Overview Originally Cargo only supported storing a registry's index within git repositories. Most git hosting solutions allow accessing a git repository with or without the `.git` suffix, so Cargo mirrored this behavior when normalizing registry URLs. This allowed credentials for `https://example.com/index` to be used for `https://example.com/index.git`. This normalization was unintentionally applied to the new sparse indexes too. Sparse indexes can be hosted on any HTTPS server, which treat URLs ending with `.git` as different URLs than those without the suffix. If the following conditions apply: * `https://example.com/index` is a sparse index. * `https://example.com/index` allows crates to depend on crates from any other registry. * The attacker is able to publish crates on `https://example.com/index`. * The attacker is able to upload arbitrary files to `https://example.com/index.git`. ...the attacker could configure `https://example.com/index.git` to be a Cargo sparse registry requiring authentication for downloads, and with a download URL pointing to a server recording any credentials set to it. When the attacker then publishes a crate `foo` to `https://example.com/index` depending on a crate `bar` from `https://example.com/index.git`, and tricks the victim into downloading `foo`, Cargo will think the two registries share the same credential and send the victim's Cargo token to the malicious registry. ## Mitigations Rust 1.96, to be released on May 28th, 2026, will update Cargo to only strip the `.git` suffix from registry URLs using the git protocol. No mitigations are available for users of older versions of Cargo. ## Affected versions All versions of Cargo shipped between Rust 1.68 (the stabilization of sparse registries) and 1.96 are affected. ## Acknowledgements Cargo would like to thank Christos Papakonstantinou for reporting this issue according to the [Rust security policy][2]. Cargo also wants to thank the members of the Rust project who helped address the vulnerability: Arlo Siemens for developing the fix; Weihang Lo, Eric Huss and Emily Albini for reviewing the fix; Emily Albini for writing this advisory; Emily Albini, Josh Stone and Manish Goregaokar for coordinating the disclosure. [1]: https://doc.rust-lang.org/cargo/reference/registries.html#registry-protocols [2]: https://rust-lang.org/policies/security