CVE-2021-39218 Detail

Current Description

Wasmtime is an open source runtime for WebAssembly & WASI. In Wasmtime from version 0.26.0 and before version 0.30.0 is affected by a memory unsoundness vulnerability. There was an invalid free and out-of-bounds read and write bug when running Wasm that uses `externref`s in Wasmtime. To trigger this bug, Wasmtime needs to be running Wasm that uses `externref`s, the host creates non-null `externrefs`, Wasmtime performs a garbage collection (GC), and there has to be a Wasm frame on the stack that is at a GC safepoint where there are no live references at this safepoint, and there is a safepoint with live references earlier in this frame's function. Under this scenario, Wasmtime would incorrectly use the GC stack map for the safepoint from earlier in the function instead of the empty safepoint. This would result in Wasmtime treating arbitrary stack slots as `externref`s that needed to be rooted for GC. At the *next* GC, it would be determined that nothing was referencing these bogus `externref`s (because nothing could ever reference them, because they are not really `externref`s) and then Wasmtime would deallocate them and run `<ExternRef as Drop>::drop` on them. This results in a free of memory that is not necessarily on the heap (and shouldn't be freed at this moment even if it was), as well as potential out-of-bounds reads and writes. Even though support for `externref`s (via the reference types proposal) is enabled by default, unless you are creating non-null `externref`s in your host code or explicitly triggering GCs, you cannot be affected by this bug. We have reason to believe that the effective impact of this bug is relatively small because usage of `externref` is currently quite rare. This bug has been patched and users should upgrade to Wasmtime version 0.30.0. If you cannot upgrade Wasmtime at this time, you can avoid this bug by disabling the reference types proposal by passing `false` to `wasmtime::Config::wasm_reference_types`.


View Analysis Description

Severity



CVSS 3.x Severity and Metrics:

Nist CVSS score does not match with CNA score
CNA:  GitHub, Inc.
Base Score:  6.3 MEDIUM
Vector:  CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H


NVD Analysts use publicly available information to associate vector strings and CVSS scores. We also display any CVSS information provided within the CVE List from the CNA.

Note: The CNA providing a score has achieved an Acceptance Level of Provider. The NVD will only audit a subset of scores provided by this CNA.

References to Advisories, Solutions, and Tools

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Hyperlink Resource
https://crates.io/crates/wasmtime Product 
https://github.com/bytecodealliance/wasmtime/commit/398a73f0dd862dbe703212ebae8e34036a18c11c Patch  Third Party Advisory 
https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-4873-36h9-wv49 Third Party Advisory 
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/WAVBRYDDUIY2ZR3K3FO4BVYJKIMJ5TP7/
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/Z2Z33FTXFQ6EOINVEQIP4DFBG53G5XIY/ Mailing List  Third Party Advisory 

Weakness Enumeration

CWE-ID CWE Name Source
CWE-590 Free of Memory not on the Heap Provider acceptance level GitHub, Inc.  
CWE-787 Out-of-bounds Write Provider acceptance level GitHub, Inc.  
CWE-125 Out-of-bounds Read Provider acceptance level GitHub, Inc.  

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Change History

3 change records found show changes

Quick Info

CVE Dictionary Entry:
CVE-2021-39218
NVD Published Date:
09/17/2021
NVD Last Modified:
10/03/2021
Source:
GitHub, Inc.