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RUSTSEC-2022-0070

Unsound API in secp256k1 allows use-after-free and invalid deallocation from safe code

Reported
Issued
Package
secp256k1 (crates.io)
Type
INFO Unsound
Categories
Keywords
#use-after-free #unsound-api #invalid-free
Details
https://github.com/rust-bitcoin/rust-secp256k1/issues/543
Patched
  • >=0.22.2, <0.23.0
  • >=0.23.5, <0.24.0
  • >=0.24.2
Unaffected
  • <0.14.0
Affected Functions
Version
secp256k1::Secp256k1::preallocated_gen_new
  • <0.22.2
  • >=0.23.0, <0.23.5
  • >=0.24.0, <0.24.2

Description

Because of incorrect bounds on method Secp256k1::preallocated_gen_new it was possible to cause use-after-free from safe consumer code. It was also possible to "free" memory not allocated by the appropriate allocator.

The method takes a place for storing the context as a mutable reference and returns context containing that reference. Because the code internally uses unsafe and the bounds were incorrect it was possible to create a context that outlived the passed reference (e.g. 'static). Because the context can alternatively carry heap-allocated pointer freed on drop it was possible to "deallocate" a pointer that wasn't returned from appropriate allocator. The code decides whether to free the memory based on type parameter but because of missing bound it was possible to construct the context with invalid parameter.

You are unaffected if you either

The patched version uses correct bounds which means it is API-breaking. This effectively means adopting the policy of Rust lang itself allowing API-breaking changes to fix soundness bugs. Note however that valid straigthforward usage of the code will continue to compile. Only unsound code or code that propagates the bound in custom generics will fail to compile. If the code is sound fixing the bounds should be sufficient to make the code compile.

See the GitHub issue for example "exploit" code and further discussion.