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WS-2023-0422

Date: August 19, 2025

Insufficient covariance check makes self_cell unsound: 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.

Language: RUST

Severity Score

Severity Score

Weakness Type (CWE)

Insufficient Verification of Data Authenticity

CWE-345

CVSS v3.1

Base Score:
Attack Vector (AV): NETWORK
Attack Complexity (AC): LOW
Privileges Required (PR): NONE
User Interaction (UI): NONE
Scope (S): UNCHANGED
Confidentiality (C): NONE
Integrity (I): HIGH
Availability (A): NONE

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