Use after free in Wasmtime

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No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

Wasmtime is a standalone JIT-style runtime for WebAssembly, using Cranelift. There is a use after free vulnerability in Wasmtime when both running Wasm that uses externrefs and enabling epoch interruption in Wasmtime. If you are not explicitly enabling epoch interruption (it is disabled by default) then you are not affected. If you are explicitly disabling the Wasm reference types proposal (it is enabled by default) then you are also not affected. The use after free is caused by Cranelift failing to emit stack maps when there are safepoints inside cold blocks. Cold blocks occur when epoch interruption is enabled. Cold blocks are emitted at the end of compiled functions, and change the order blocks are emitted versus defined. This reordering accidentally caused Cranelift to skip emitting some stack maps because it expected to emit the stack maps in block definition order, rather than block emission order. When Wasmtime would eventually collect garbage, it would fail to find live references on the stack because of the missing stack maps, think that they were unreferenced garbage, and therefore reclaim them. Then after the collection ended, the Wasm code could use the reclaimed-too-early references, which is a use after free. Patches have been released in versions 0.34.2 and 0.35.2, which fix the vulnerability. All Wasmtime users are recommended to upgrade to these patched versions. If upgrading is not an option for you at this time, you can avoid the vulnerability by either: disabling the Wasm reference types proposal, config.wasm_reference_types(false); or by disabling epoch interruption if you were previously enabling it. config.epoch_interruption(false).

Source published

31 Mar 2022 23:00:15 UTC

Source modified

23 Apr 2025 18:42:35 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 3.1 · 8.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Wasmtime is a standalone JIT-style runtime for WebAssembly, using Cranelift. There is a use after free vulnerability in Wasmtime when both running Wasm that uses externrefs and enabling epoch interruption in Wasmtime. If you are not explicitly enabling epoch interruption (it is disabled by default) then you are not affected. If you are explicitly disabling the Wasm reference types proposal (it is enabled by default) then you are also not affected. The use after free is caused by Cranelift failing to emit stack maps when there are safepoints inside cold blocks. Cold blocks occur when epoch interruption is enabled. Cold blocks are emitted at the end of compiled functions, and change the order blocks are emitted versus defined. This reordering accidentally caused Cranelift to skip emitting some stack maps because it expected to emit the stack maps in block definition order, rather than block emission order. When Wasmtime would eventually collect garbage, it would fail to find live references on the stack because of the missing stack maps, think that they were unreferenced garbage, and therefore reclaim them. Then after the collection ended, the Wasm code could use the reclaimed-too-early references, which is a use after free. Patches have been released in versions 0.34.2 and 0.35.2, which fix the vulnerability. All Wasmtime users are recommended to upgrade to these patched versions. If upgrading is not an option for you at this time, you can avoid the vulnerability by either: disabling the Wasm reference types proposal, config.wasm_reference_types(false); or by disabling epoch interruption if you were previously enabling it. config.epoch_interruption(false).

Source published

Mar 31, 2022, 11:00:15 PM (timezone not stated)

Source modified

Apr 23, 2025, 6:42:35 PM (timezone not stated)

Observed here

9 Nov 2026 23:15:46 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 3.1 · 8.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Wasmtime is a standalone JIT-style runtime for WebAssembly, using Cranelift. There is a use after free vulnerability in Wasmtime when both running Wasm that uses externrefs and enabling epoch interruption in Wasmtime. If you are not explicitly enabling epoch interruption (it is disabled by default) then you are not affected. If you are explicitly disabling the Wasm reference types proposal (it is enabled by default) then you are also not affected. The use after free is caused by Cranelift failing to emit stack maps when there are safepoints inside cold blocks. Cold blocks occur when epoch interruption is enabled. Cold blocks are emitted at the end of compiled functions, and change the order blocks are emitted versus defined. This reordering accidentally caused Cranelift to skip emitting some stack maps because it expected to emit the stack maps in block definition order, rather than block emission order. When Wasmtime would eventually collect garbage, it would fail to find live references on the stack because of the missing stack maps, think that they were unreferenced garbage, and therefore reclaim them. Then after the collection ended, the Wasm code could use the reclaimed-too-early references, which is a use after free. Patches have been released in versions 0.34.2 and 0.35.2, which fix the vulnerability. All Wasmtime users are recommended to upgrade to these patched versions. If upgrading is not an option for you at this time, you can avoid the vulnerability by either: disabling the Wasm reference types proposal, config.wasm_reference_types(false); or by disabling epoch interruption if you were previously enabling it. config.epoch_interruption(false).

Source published

31 Mar 2022 23:15:08 UTC

Source modified

17 Jun 2026 04:32:31 UTC

Observed here

24 Oct 2026 20:17:12 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 8.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS 3.1 · [email protected] · Primary · 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS 2.0 · [email protected] · Primary · 6.8 AV:N/AC:M/Au:N/C:P/I:P/A:P

There is a use after free vulnerability in Wasmtime when both running Wasm that uses `externref`s and enabling [epoch interruption](https://docs.rs/wasmtime/latest/wasmtime/struct.Config.html#method.epoch_interruption) in Wasmtime. If you are not explicitly enabling epoch interruption (it is disabled by default) then you are not affected. If you are explicitly disabling the Wasm reference types proposal (it is enabled by default) then you are also not affected. The use after free is caused by Cranelift failing to emit stack maps when there are safepoints inside cold blocks. Cold blocks occur when epoch interruption is enabled. Cold blocks are emitted at the end of compiled functions, and change the order blocks are emitted versus defined. This reordering accidentally caused Cranelift to skip emitting some stack maps because it expected to emit the stack maps in block definition order, rather than block emission order. When Wasmtime would eventually collect garbage, it would fail to find live references on the stack because of the missing stack maps, think that they were unreferenced garbage, and therefore reclaim them. Then after the collection ended, the Wasm code could use the reclaimed-too-early references, which is a use after free. This bug was discovered while extending our fuzz targets for `externref`s and GC in Wasmtime. The updated fuzz target thoroughly exercises these code paths and feature combinations now. We have also added a regression test for this bug. Released versions 0.34.2 and 0.35.2, which fix the vulnerability. We recommend all Wasmtime users upgrade to these patched versions. If upgrading is not an option for you at this time, you can avoid the vulnerability by either disabling the Wasm reference types proposal or by disabling epoch interruption if you were previously enabling it.

Source published

1 Apr 2022 13:36:12 UTC

Source modified

2 May 2025 12:48:46 UTC

Observed here

24 Oct 2026 13:19:54 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Publisher rating · HIGH

[Use after free with `externref`s and epoch interruption in Wasmtime](https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-gwc9-348x-qwv2)

Source published

31 Mar 2022 12:00:00 UTC

Source modified

12 Oct 2026 18:00:03 UTC

Observed here

24 Oct 2026 13:19:54 UTC

Source terms

OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.

This is an entry in the RustSec database for the Wasmtime security advisory located at https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-gwc9-348x-qwv2. For more information see the GitHub-hosted security advisory.

Source published

28 Mar 2022 12:00:00 UTC

Source modified

12 Oct 2026 18:00:03 UTC

Observed here

24 Oct 2026 13:19:54 UTC

Source terms

OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.