{"id":"GHSA-f5v5-ccqc-6w36","aliases":["RUSTSEC-2023-0027"],"status":"published","title":"async-nats vulnerable to TLS certificate common name validation bypass","description":"The NATS official Rust clients are vulnerable to MitM when using TLS.\n\nThe common name of the server's TLS certificate is validated against the `host`name provided by the server's plaintext `INFO` message during the initial connection setup phase. A MitM proxy can tamper with the `host` field's value by substituting it with the common name of a valid certificate it controls, fooling the client into accepting it.\n\n## Reproduction steps\n\n1. The NATS Rust client tries to establish a new connection\n2. The connection is intercepted by a MitM proxy\n3. The proxy makes a separate connection to the NATS server\n4. The NATS server replies with an `INFO` message\n5. The proxy reads the `INFO`, alters the `host` JSON field and passes the tampered `INFO` back to the client\n6. The proxy upgrades the client connection to TLS, presenting a certificate issued by a certificate authority present in the client's keychain. In the previous step the `host` was set to the common name of said certificate\n7. `rustls` accepts the certificate, having verified that the common name matches the attacker-controlled value it was given\n8. The client has been fooled by the MitM proxy into accepting the attacker-controlled certificate","facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"published":"2023-03-24T12:00:00Z","modified":"2023-11-08T04:18:50Z","fixes":[{"ecosystem":"crates.io","package":"async-nats","fixed_in":["0.29.0"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"crates.io","package":"async-nats","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.29.0"}]}]},{"source":"osv","ecosystem":"crates.io","package":"async-nats","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"0.29.0"}]}]},{"source":"osv","ecosystem":"crates.io","package":"async-nats","ranges":[{"type":"SEMVER","events":[{"introduced":"0.0.0-0"},{"fixed":"0.29.0"}]}]}],"references":[{"url":"https://github.com/nats-io/nats.rs/commit/817a7b942c462fa9d9938dcb62124173634132fb#diff-767d442397fcaaf2f83e8f924d4a70317a2ce4703a49964d6007707949cfa5f5L303-R304","tags":["web"]},{"url":"https://rustsec.org/advisories/RUSTSEC-2023-0027.html","tags":["web","advisory"]},{"url":"https://github.com/advisories/GHSA-f5v5-ccqc-6w36"},{"url":"https://github.com/nats-io/nats.rs","tags":["package"]},{"url":"https://crates.io/crates/async-nats","tags":["package"]}],"sources":{"ghsa":[{"id":"GHSA-f5v5-ccqc-6w36","title":"async-nats vulnerable to TLS certificate common name validation bypass","description":"The NATS official Rust clients are vulnerable to MitM when using TLS.\n\nThe common name of the server's TLS certificate is validated against the `host`name provided by the server's plaintext `INFO` message during the initial connection setup phase. A MitM proxy can tamper with the `host` field's value by substituting it with the common name of a valid certificate it controls, fooling the client into accepting it.\n\n## Reproduction steps\n\n1. The NATS Rust client tries to establish a new connection\n2. The connection is intercepted by a MitM proxy\n3. The proxy makes a separate connection to the NATS server\n4. The NATS server replies with an `INFO` message\n5. The proxy reads the `INFO`, alters the `host` JSON field and passes the tampered `INFO` back to the client\n6. The proxy upgrades the client connection to TLS, presenting a certificate issued by a certificate authority present in the client's keychain. In the previous step the `host` was set to the common name of said certificate\n7. `rustls` accepts the certificate, having verified that the common name matches the attacker-controlled value it was given\n8. The client has been fooled by the MitM proxy into accepting the attacker-controlled certificate\n","status":"published","published":"2023-03-24T21:59:53Z","modified":"2023-03-24T21:59:54Z","updated_at":"2026-11-02T14:36:48.905887Z"}],"osv":[{"id":"GHSA-f5v5-ccqc-6w36","title":"async-nats vulnerable to TLS certificate common name validation bypass","description":"The NATS official Rust clients are vulnerable to MitM when using TLS.\n\nThe common name of the server's TLS certificate is validated against the `host`name provided by the server's plaintext `INFO` message during the initial connection setup phase. A MitM proxy can tamper with the `host` field's value by substituting it with the common name of a valid certificate it controls, fooling the client into accepting it.\n\n## Reproduction steps\n\n1. The NATS Rust client tries to establish a new connection\n2. The connection is intercepted by a MitM proxy\n3. The proxy makes a separate connection to the NATS server\n4. The NATS server replies with an `INFO` message\n5. The proxy reads the `INFO`, alters the `host` JSON field and passes the tampered `INFO` back to the client\n6. The proxy upgrades the client connection to TLS, presenting a certificate issued by a certificate authority present in the client's keychain. In the previous step the `host` was set to the common name of said certificate\n7. `rustls` accepts the certificate, having verified that the common name matches the attacker-controlled value it was given\n8. The client has been fooled by the MitM proxy into accepting the attacker-controlled certificate\n","status":"published","published":"2023-03-24T21:59:53Z","modified":"2023-11-08T04:18:50.21049Z","updated_at":"2026-11-02T15:46:46.006631Z"},{"id":"RUSTSEC-2023-0027","title":"TLS certificate common name validation bypass","description":"The NATS official Rust clients are vulnerable to MitM when using TLS.\n\nThe common name of the server's TLS certificate is validated against\nthe `host`name provided by the server's plaintext `INFO` message\nduring the initial connection setup phase. A MitM proxy can tamper with\nthe `host` field's value by substituting it with the common name of a\nvalid certificate it controls, fooling the client into accepting it.\n\n## Reproduction steps\n\n1. The NATS Rust client tries to establish a new connection\n2. The connection is intercepted by a MitM proxy\n3. The proxy makes a separate connection to the NATS server\n4. The NATS server replies with an `INFO` message\n5. The proxy reads the `INFO`, alters the `host` JSON field and passes\n   the tampered `INFO` back to the client\n6. The proxy upgrades the client connection to TLS, presenting a certificate issued\n   by a certificate authority present in the client's keychain.\n   In the previous step the `host` was set to the common name of said certificate\n7. `rustls` accepts the certificate, having verified that the common name matches the\n   attacker-controlled value it was given\n9. The client has been fooled by the MitM proxy into accepting the attacker-controlled certificate","status":"published","published":"2023-03-24T12:00:00Z","modified":"2023-11-08T04:18:50.21049Z","updated_at":"2026-11-02T15:53:39.971022Z"}]}}