require capsule destructor closures to be 'static#6049
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May 16, 2026
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It's very likely that code which accidentally did this would crash in test suites, and the fact nobody reported this probably means it doesn't exist in the wild
Agreed. This is the kind of thing that is not checked at all by C/C++ and wouldn't be a CVE there.
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It turns out that while we have
T: 'staticrequirements on capsule constructors, for the variants which also acceptFtype parameters for destructors we lackF: 'static.This of course means that it's possible to define a destructor which captures data by-reference from the stack, which will most likely lead to instant segfault when the destructor runs on capsule cleanup.
I am undecided whether this is a severe enough issue that it warrants reporting to the Rust advisory-db; on the one hand it's very likely that code which accidentally did this would crash in test suites, and the fact nobody reported this probably means it doesn't exist in the wild. On the other hand, it is possible that there are accidental UAFs implemented in user code due to this gap. Opinions welcome.
(Credit to Codex security scanning for this discovery.)