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What is the vulnerability?
The Rust standard library contains the `Error::type_id` method, which allows you to acquire TypeId (a globally unique identifier for a type) of the underlying error type to downcast back to the original type. The vulnerability happens when the method is manually implemented or interacts with ‘Error::downcast’ family of functions to cast a type to the wrong type.
Though the standard library has a default implementation of ‘Error::type_id’, it can also be manually implemented by downstream crates. This can cause security issues such as out of bounds reads and writes. If your code does not have a manual implementation of ‘Error::type_id’, then it is safe.
This vulnerability affects two versions, Rust 1.34.0 and 1.34.1, which were released last month. Also, since the function has been a part of all the releases starting from Rust 1.0.0, this vulnerability may have affected the code compiled with the nightly distribution as well.
What are the mitigation steps?
The Rust team recommends to immediately remove the manual implementations of Error::type_id and inherit the default implementation which is a safe option. As a long term measure, the team plans to destabilize this function, which will be a breaking change for users calling Error::type_id and for users overriding Error::type_id.
The team further wrote, “We will be releasing a 1.34.2 point release on 2019-05-14 (tomorrow) which reverts #58048 and destabilizes the Error::type_id function. The upcoming 1.35.0 release along with the beta/nightly channels will also all be updated with a destabilization.”
Read the full announcement on Rust’s official website.