Advisory Published


First published: Tue Nov 14 2023(Updated: )

All public versions prior to `1.02` used an insufficient check to ensure that users correctly marked the dependent type as either `covariant` or `not_covariant`. This allowed users to mark a dependent as covariant even though its type was not covariant but invariant, for certain invariant types involving trait object lifetimes. One example for such a dependent type is `type Dependent<'a> = RefCell<Box<dyn fmt::Display + 'a>>`. Such a type allowed unsound usage in purely safe user code that leads to undefined behavior. The patched versions now produce a compile time error if such a type is marked as `covariant`.

Affected SoftwareAffected VersionHow to fix

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Frequently Asked Questions

  • What is the vulnerability ID?

    The vulnerability ID is GHSA-48m6-wm5p-rr6h.

  • What is the title of the vulnerability?

    The title of the vulnerability is 'All public versions prior to `1.02` used an insufficient check to ensure that users correctly marked...'

  • What software versions are affected?

    All public versions prior to 1.02 are affected.

  • How can I fix this vulnerability?

    To fix this vulnerability, update to version 1.02 or higher.

  • Are there any references I can check for more information?

    Yes, you can check the following references for more information: [GitHub issue #49](, [RustSec advisory RUSTSEC-2023-0070](, [GitHub advisory GHSA-48m6-wm5p-rr6h](


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