| Vulnerability Name: | CVE-2021-39218 (CCN-209627) | ||||||||||||
| Assigned: | 2021-09-17 | ||||||||||||
| Published: | 2021-09-17 | ||||||||||||
| Updated: | 2021-12-10 | ||||||||||||
| Summary: | 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`. | ||||||||||||
| CVSS v3 Severity: | 6.3 Medium (CVSS v3.1 Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H) 5.5 Medium (Temporal CVSS v3.1 Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H/E:U/RL:O/RC:C)
5.5 Medium (CCN Temporal CVSS v3.1 Vector: CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:H/E:U/RL:O/RC:C)
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| CVSS v2 Severity: | 3.3 Low (CVSS v2 Vector: AV:L/AC:M/Au:N/C:N/I:P/A:P)
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| Vulnerability Type: | CWE-125 CWE-787 CWE-590 | ||||||||||||
| Vulnerability Consequences: | Bypass Security | ||||||||||||
| References: | Source: MITRE Type: CNA CVE-2021-39218 Source: MISC Type: Product, Third Party Advisory https://crates.io/crates/wasmtime Source: XF Type: UNKNOWN wasmtime-cve202139218-sec-bypass(209627) Source: CCN Type: Wasmtime GIT Repository Wasmtime Source: MISC Type: Patch, Third Party Advisory https://github.com/bytecodealliance/wasmtime/commit/398a73f0dd862dbe703212ebae8e34036a18c11c Source: CCN Type: Wasmtime GIT Repository Out-of-bounds read/write and invalid free with `externref`s and GC safepoints in Wasmtime Source: CONFIRM Type: Third Party Advisory https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-4873-36h9-wv49 Source: FEDORA Type: Mailing List, Third Party Advisory FEDORA-2021-1805eacb48 Source: FEDORA Type: Mailing List, Third Party Advisory FEDORA-2021-68713440cb | ||||||||||||
| Vulnerable Configuration: | Configuration 1: Configuration 2:  Denotes that component is vulnerable | ||||||||||||
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