CVE-2021-39216 Information

Description

Wasmtime is an open source runtime for WebAssembly & WASI. In Wasmtime from version 0.19.0 and before version 0.30.0 there was a use-after-free bug when passing externrefs from the host to guest Wasm content. To trigger the bug you have to explicitly pass multiple externrefs from the host to a Wasm instance at the same time either by passing multiple externrefs as arguments from host code to a Wasm function or returning multiple externrefs to Wasm from a multi-value return function defined in the host. If you do not have host code that matches one of these shapes then you are not impacted. If Wasmtime’s VMExternRefActivationsTable became filled to capacity after passing the first externref in then passing in the second externref could trigger a garbage collection. However the first externref is not rooted until we pass control to Wasm and therefore could be reclaimed by the collector if nothing else was holding a reference to it or otherwise keeping it alive. Then when control was passed to Wasm after the garbage collection Wasm could use the first externref which at this point has already been freed. We have reason to believe that the effective impact of this bug is relatively small because usage of externref is currently quite rare. The bug has been fixed and users should upgrade to Wasmtime 0.30.0. If you cannot upgrade Wasmtime yet you can avoid the bug by disabling reference types support in Wasmtime by passing false to wasmtime::Config::wasm_reference_types.

CVSS Vector

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H

Reference

https://crates.io/crates/wasmtime https://github.com/bytecodealliance/wasmtime/commit/101998733b74624cbd348a2366d05760b40181f3 https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-v4cp-h94r-m7xf https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/Z2Z33FTXFQ6EOINVEQIP4DFBG53G5XIY/ https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/WAVBRYDDUIY2ZR3K3FO4BVYJKIMJ5TP7/

Attack Complexity

HIGH

Privileges Required

LOW

User Interaction Required

LOW

Scope

NONE

Confidentiality Impact

UNCHANGED

Integrity Impact

NONE

Availability Impact

HIGH

Base Score

HIGH

Base Severity

6.3