GHSA-h97m-ww89-6jmq `idna` accepts Punycode labels that do not produce any non-ASCII when decoded

• crates.io idna: < 1.0.0 → fixed in 1.0.0

`idna` 0.5.0 and earlier accepts Punycode labels that do not produce any non-ASCII output, which means that either ASCII labels or the empty root label can be masked such that they appear unequal without IDNA processing or when processed with a different implementation and equal when processed with `idna` 0.5.0 or earlier. Concretely, `example.org` and `xn--example-.org` become equal after processing by `idna` 0.5.0 or earlier. Also, `example.org.xn--` and `example.org.` become equal after processing by `idna` 0.5.0 or earlier. In applications using `idna` (but not in `idna` itself) this may be able to lead to privilege escalation when host name comparison is part of a privilege check and the behavior is combined with a client that resolves domains with such labels instead of treating them as errors that preclude DNS resolution / URL fetching and with the attacker managing to introduce a DNS entry (and TLS certificate) for an `xn--`-masked name that turns into the name of the target when processed by `idna` 0.5.0 or earlier. Remedy Upgrade to `idna` 1.0.3 or later, if depending on `idna` directly, or to `url` 2.5.4 or later, if depending on `idna` via `url`. (This issue was fixed in `idna` 1.0.0, but versions earlier than 1.0.3 are not recommended for other reasons.) When upgrading, please take a moment to read about alternative Unicode back ends for `idna`. If you are using Rust earlier than 1.81 in combination with SQLx 0.8.2 or earlier, please also read an issue about combining them with `url` 2.5.4 and `idna` 1.0.3. Additional information This issue resulted from `idna` 0.5.0 and earlier implementing the UTS 46 specification literally on this point and the specification having this bug. The specification bug has been fixed in revision 33 of UTS 46. Acknowledgements Thanks to kageshiron for recognizing the security implications of this behavior.