Wasmtime race condition could lead to WebAssembly control-flow integrity and type safety violations

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

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

Wasmtime is an open source runtime for WebAssembly. Under certain concurrent event orderings, a `wasmtime::Engine`'s internal type registry was susceptible to double-unregistration bugs due to a race condition, leading to panics and potentially type registry corruption. That registry corruption could, following an additional and particular sequence of concurrent events, lead to violations of WebAssembly's control-flow integrity (CFI) and type safety. Users that do not use `wasmtime::Engine` across multiple threads are not affected. Users that only create new modules across threads over time are additionally not affected. Reproducing this bug requires creating and dropping multiple type instances (such as `wasmtime::FuncType` or `wasmtime::ArrayType`) concurrently on multiple threads, where all types are associated with the same `wasmtime::Engine`. **Wasm guests cannot trigger this bug.** See the "References" section below for a list of Wasmtime types-related APIs that are affected. Wasmtime maintains an internal registry of types within a `wasmtime::Engine` and an engine is shareable across threads. Types can be created and referenced through creation of a `wasmtime::Module`, creation of `wasmtime::FuncType`, or a number of other APIs where the host creates a function (see "References" below). Each of these cases interacts with an engine to deduplicate type information and manage type indices that are used to implement type checks in WebAssembly's `call_indirect` function, for example. This bug is a race condition in this management where the internal type registry could be corrupted to trigger an assert or contain invalid state. Wasmtime's internal representation of a type has individual types (e.g. one-per-host-function) maintain a registration count of how many time it's been used. Types additionally have state within an engine behind a read-write lock such as lookup/deduplication information. The race here is a time-of-check versus time-of-use (TOCTOU) bug where one thread atomically decrements a type entry's registration count, observes zero registrations, and then acquires a lock in order to unregister that entry. However, between when this first thread observed the zero-registration count and when it acquires that lock, another thread could perform the following sequence of events: re-register another copy of the type, which deduplicates to that same entry, resurrecting it and incrementing its registration count; then drop the type and decrement its registration count; observe that the registration count is now zero; acquire the type registry lock; and finally unregister the type. Now, when the original thread finally acquires the lock and unregisters the entry, it is the second time this entry has been unregistered. This bug was originally introduced in Wasmtime 19's development of the WebAssembly GC proposal. This bug affects users who are not using the GC proposal, however, and affects Wasmtime in its default configuration even when the GC proposal is disabled. Wasmtime users using 19.0.0 and after are all affected by this issue. We have released the following Wasmtime versions, all of which have a fix for this bug: * 21.0.2 * 22.0.1 * 23.0.3 * 24.0.1 * 25.0.2. If your application creates and drops Wasmtime types on multiple threads concurrently, there are no known workarounds. Users are encouraged to upgrade to a patched release.

Source published

9 Oct 2024 18:07:49 UTC

Source modified

9 Oct 2024 19:43:53 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · 2.9 CVSS:3.1/AV:L/AC:H/PR:H/UI:R/S:U/C:N/I:L/A:L

Wasmtime is an open source runtime for WebAssembly. Under certain concurrent event orderings, a `wasmtime::Engine`'s internal type registry was susceptible to double-unregistration bugs due to a race condition, leading to panics and potentially type registry corruption. That registry corruption could, following an additional and particular sequence of concurrent events, lead to violations of WebAssembly's control-flow integrity (CFI) and type safety. Users that do not use `wasmtime::Engine` across multiple threads are not affected. Users that only create new modules across threads over time are additionally not affected. Reproducing this bug requires creating and dropping multiple type instances (such as `wasmtime::FuncType` or `wasmtime::ArrayType`) concurrently on multiple threads, where all types are associated with the same `wasmtime::Engine`. **Wasm guests cannot trigger this bug.** See the "References" section below for a list of Wasmtime types-related APIs that are affected. Wasmtime maintains an internal registry of types within a `wasmtime::Engine` and an engine is shareable across threads. Types can be created and referenced through creation of a `wasmtime::Module`, creation of `wasmtime::FuncType`, or a number of other APIs where the host creates a function (see "References" below). Each of these cases interacts with an engine to deduplicate type information and manage type indices that are used to implement type checks in WebAssembly's `call_indirect` function, for example. This bug is a race condition in this management where the internal type registry could be corrupted to trigger an assert or contain invalid state. Wasmtime's internal representation of a type has individual types (e.g. one-per-host-function) maintain a registration count of how many time it's been used. Types additionally have state within an engine behind a read-write lock such as lookup/deduplication information. The race here is a time-of-check versus time-of-use (TOCTOU) bug where one thread atomically decrements a type entry's registration count, observes zero registrations, and then acquires a lock in order to unregister that entry. However, between when this first thread observed the zero-registration count and when it acquires that lock, another thread could perform the following sequence of events: re-register another copy of the type, which deduplicates to that same entry, resurrecting it and incrementing its registration count; then drop the type and decrement its registration count; observe that the registration count is now zero; acquire the type registry lock; and finally unregister the type. Now, when the original thread finally acquires the lock and unregisters the entry, it is the second time this entry has been unregistered. This bug was originally introduced in Wasmtime 19's development of the WebAssembly GC proposal. This bug affects users who are not using the GC proposal, however, and affects Wasmtime in its default configuration even when the GC proposal is disabled. Wasmtime users using 19.0.0 and after are all affected by this issue. We have released the following Wasmtime versions, all of which have a fix for this bug: * 21.0.2 * 22.0.1 * 23.0.3 * 24.0.1 * 25.0.2. If your application creates and drops Wasmtime types on multiple threads concurrently, there are no known workarounds. Users are encouraged to upgrade to a patched release.

Source published

Oct 9, 2024, 6:07:49 PM (timezone not stated)

Source modified

Oct 9, 2024, 7:43:53 PM (timezone not stated)

Observed here

9 Nov 2026 01:07:34 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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

Wasmtime is an open source runtime for WebAssembly. Under certain concurrent event orderings, a `wasmtime::Engine`'s internal type registry was susceptible to double-unregistration bugs due to a race condition, leading to panics and potentially type registry corruption. That registry corruption could, following an additional and particular sequence of concurrent events, lead to violations of WebAssembly's control-flow integrity (CFI) and type safety. Users that do not use `wasmtime::Engine` across multiple threads are not affected. Users that only create new modules across threads over time are additionally not affected. Reproducing this bug requires creating and dropping multiple type instances (such as `wasmtime::FuncType` or `wasmtime::ArrayType`) concurrently on multiple threads, where all types are associated with the same `wasmtime::Engine`. **Wasm guests cannot trigger this bug.** See the "References" section below for a list of Wasmtime types-related APIs that are affected. Wasmtime maintains an internal registry of types within a `wasmtime::Engine` and an engine is shareable across threads. Types can be created and referenced through creation of a `wasmtime::Module`, creation of `wasmtime::FuncType`, or a number of other APIs where the host creates a function (see "References" below). Each of these cases interacts with an engine to deduplicate type information and manage type indices that are used to implement type checks in WebAssembly's `call_indirect` function, for example. This bug is a race condition in this management where the internal type registry could be corrupted to trigger an assert or contain invalid state. Wasmtime's internal representation of a type has individual types (e.g. one-per-host-function) maintain a registration count of how many time it's been used. Types additionally have state within an engine behind a read-write lock such as lookup/deduplication information. The race here is a time-of-check versus time-of-use (TOCTOU) bug where one thread atomically decrements a type entry's registration count, observes zero registrations, and then acquires a lock in order to unregister that entry. However, between when this first thread observed the zero-registration count and when it acquires that lock, another thread could perform the following sequence of events: re-register another copy of the type, which deduplicates to that same entry, resurrecting it and incrementing its registration count; then drop the type and decrement its registration count; observe that the registration count is now zero; acquire the type registry lock; and finally unregister the type. Now, when the original thread finally acquires the lock and unregisters the entry, it is the second time this entry has been unregistered. This bug was originally introduced in Wasmtime 19's development of the WebAssembly GC proposal. This bug affects users who are not using the GC proposal, however, and affects Wasmtime in its default configuration even when the GC proposal is disabled. Wasmtime users using 19.0.0 and after are all affected by this issue. We have released the following Wasmtime versions, all of which have a fix for this bug: * 21.0.2 * 22.0.1 * 23.0.3 * 24.0.1 * 25.0.2. If your application creates and drops Wasmtime types on multiple threads concurrently, there are no known workarounds. Users are encouraged to upgrade to a patched release.

Source published

9 Oct 2024 18:15:09 UTC

Source modified

17 Jun 2026 07:57:47 UTC

Observed here

25 Oct 2026 00:17:35 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 · 2.9 CVSS:3.1/AV:L/AC:H/PR:H/UI:R/S:U/C:N/I:L/A:L

### Impact Under certain concurrent event orderings, a `wasmtime::Engine`'s internal type registry was susceptible to double-unregistration bugs due to a race condition, leading to panics and potentially type registry corruption. That registry corruption could, following an additional and particular sequence of concurrent events, lead to violations of WebAssembly's control-flow integrity (CFI) and type safety. Users that do not use `wasmtime::Engine` across multiple threads are not affected. Users that only create new modules across threads over time are additionally not affected. Reproducing this bug requires creating and dropping multiple type instances (such as `wasmtime::FuncType` or `wasmtime::ArrayType`) concurrently on multiple threads, where all types are associated with the same `wasmtime::Engine`. **Wasm guests cannot trigger this bug.** See the "References" section below for a list of Wasmtime types-related APIs that are affected. Wasmtime maintains an internal registry of types within a `wasmtime::Engine` and an engine is shareable across threads. Types can be created and referenced through creation of a `wasmtime::Module`, creation of `wasmtime::FuncType`, or a number of other APIs where the host creates a function (see "References" below). Each of these cases interacts with an engine to deduplicate type information and manage type indices that are used to implement type checks in WebAssembly's `call_indirect` function, for example. This bug is a race condition in this management where the internal type registry could be corrupted to trigger an assert or contain invalid state. Wasmtime's internal representation of a type has individual types (e.g. one-per-host-function) maintain a registration count of how many time it's been used. Types additionally have state within an engine behind a read-write lock such as lookup/deduplication information. The race here is a time-of-check versus time-of-use (TOCTOU) bug where one thread atomically decrements a type entry's registration count, observes zero registrations, and then acquires a lock in order to unregister that entry. However, between when this first thread observed the zero-registration count and when it acquires that lock, another thread could perform the following sequence of events: re-register another copy of the type, which deduplicates to that same entry, resurrecting it and incrementing its registration count; then drop the type and decrement its registration count; observe that the registration count is now zero; acquire the type registry lock; and finally unregister the type. Now, when the original thread finally acquires the lock and unregisters the entry, it is the second time this entry has been unregistered. | Thread A | Thread B | |-----------------------------------|--------------------------------| | `acquire(type registry lock)` | | | | `decref(E) --> 0` | | | `block_on(type registry lock)` | | `register(E') == incref(E) --> 1` | | | `release(type registry lock)` | | | `decref(E) --> 0` | | | `acquire(type registry lock)` | | | `unregister(E)` | | | `release(type registry lock)` | | | | `acquire(type registry lock)` | | | `unregister(E)` | This double-unregistration could then lead to a WebAssembly CFI violation under the following conditions: a new WebAssembly module `X` was loaded into the engine before the second, buggy unregistration occurs; `X` defined a function type `F` that was allocated in the same type registry slot where the original entry was allocated; the second, buggy unregistration incorrectly unregistered `F`; another new WebAssembly module `Y` was loaded into the engine; `Y` defined a function type `G`, different from `F`, but which is also allocated in the same type registry slot; a `funcref` of type `G` is created, either by the host or by Wasm; that `funcref` is passed to a WebAssembly instance of module `X`; that instance performs a `call_indirect` to that `funcref`; the `call_indirect`'s dynamic type check, which preserves CFI, could incorrectly pass in this case, because `F` and `G` were assigned the same type registry slot. This would, ultimately, allow calling a function with too many, too few, or wrongly-typed arguments, violating CFI and type safety. We were not able to reproduce this CFI violation in a vanilla Wasmtime build, although it remains theoretically possible. However, by modifying Wasmtime's source code to make losing the races described above more likely (by disabling certain assertions, inserting panic catches, and adding retry loops in a few places if we did *not* lose the race) we were able to incorrectly get a `funcref` to pass a type check that it should have failed, which would allow the CFI violation. ### Patches This bug was originally introduced in Wasmtime 19's development of the WebAssembly GC proposal. This bug affects users who are not using the GC proposal, however, and affects Wasmtime in its default configuration even when the GC proposal is disabled. Wasmtime users using 19.0.0 and after are all affected by this issue. We have released the following Wasmtime versions, all of which have a fix for this bug: * 21.0.2 * 22.0.1 * 23.0.3 * 24.0.1 * 25.0.2 ### Workarounds If your application creates and drops Wasmtime types on multiple threads concurrently, there are no known workarounds. Users are encouraged to upgrade to a patched release. ### References The following APIs create or drop types, and therefore are affected by this race condition if performed on multiple threads concurrently and are all associated with the same `wasmtime::Engine`: * [`wasmtime::FuncType::new`](https://docs.rs/wasmtime/latest/wasmtime/struct.FuncType.html#method.new) * Also reachable from creation of [`wasmtime::Func`](https://docs.rs/wasmtime/latest/wasmtime/struct.Func.html) * Also reachable from [`wasmtime::Linker::func_*`](https://docs.rs/wasmtime/latest/wasmtime/struct.Linker.html#method.func_new) * [`wasmtime::ArrayType::new`](https://docs.rs/wasmtime/latest/wasmtime/struct.ArrayType.html#method.new) * [`wasmtime::StructType::new`](https://docs.rs/wasmtime/latest/wasmtime/struct.StructType.html#method.new) * [`wasmtime::Func::ty`](https://docs.rs/wasmtime/latest/wasmtime/struct.Func.html#method.ty) * [`wasmtime::Global::ty`](https://docs.rs/wasmtime/latest/wasmtime/struct.Global.html#method.ty) * [`wasmtime::Table::ty`](https://docs.rs/wasmtime/latest/wasmtime/struct.Table.html#method.ty) * [`wasmtime::Extern::ty`](https://docs.rs/wasmtime/latest/wasmtime/struct.Extern.html#method.ty) * [`wasmtime::Export::ty`](https://docs.rs/wasmtime/latest/wasmtime/struct.Export.html#method.ty) * [`wasmtime::UnknownImportError::ty`](https://docs.rs/wasmtime/latest/wasmtime/struct.UnknownImportError.html#method.ty) * [`wasmtime::ImportType::ty`](https://docs.rs/wasmtime/latest/wasmtime/struct.ImportType.html#method.ty) * [`wasmtime::ExportType::ty`](https://docs.rs/wasmtime/latest/wasmtime/struct.ExportType.html#method.ty) * [`wasmtime::Val::ty`](https://docs.rs/wasmtime/latest/wasmtime/struct.Val.html#method.ty) * [`wasmtime::Ref::ty`](https://docs.rs/wasmtime/latest/wasmtime/struct.Ref.html#method.ty) * [`wasmtime::AnyRef::ty`](https://docs.rs/wasmtime/latest/wasmtime/struct.AnyRef.html#method.ty) * [`wasmtime::EqRef::ty`](https://docs.rs/wasmtime/latest/wasmtime/struct.EqRef.html#method.ty) * [`wasmtime::ArrayRef::ty`](https://docs.rs/wasmtime/latest/wasmtime/struct.ArrayRef.html#method.ty) * [`wasmtime::StructRef::ty`](https://docs.rs/wasmtime/latest/wasmtime/struct.StructRef.html#method.ty) * Dropping a [`wasmtime::FuncType`](https://docs.rs/wasmtime/latest/wasmtime/struct.FuncType.html) * Dropping a [`wasmtime::ArrayType`](https://docs.rs/wasmtime/latest/wasmtime/struct.ArrayType.html) * Dropping a [`wasmtime::StructType`](https://docs.rs/wasmtime/latest/wasmtime/struct.StructType.html) * Dropping a [`wasmtime::ExternType`](https://docs.rs/wasmtime/latest/wasmtime/struct.ExternType.html) * Dropping a [`wasmtime::GlobalType`](https://docs.rs/wasmtime/latest/wasmtime/struct.GlobalType.html) * Dropping a [`wasmtime::TableType`](https://docs.rs/wasmtime/latest/wasmtime/struct.TableType.html) * Dropping a [`wasmtime::ValType`](https://docs.rs/wasmtime/latest/wasmtime/struct.ValType.html) * Dropping a [`wasmtime::RefType`](https://docs.rs/wasmtime/latest/wasmtime/struct.RefType.html) * Dropping a [`wasmtime::HeapType`](https://docs.rs/wasmtime/latest/wasmtime/struct.HeapType.html) * Dropping a [`wasmtime::UnknownImportError`](https://docs.rs/wasmtime/latest/wasmtime/struct.UnknownImportError.html) * Dropping a [`wasmtime::Linker`](https://docs.rs/wasmtime/latest/wasmtime/struct.Linker.html) The change which introduced this bug was [#7969](https://github.com/bytecodealliance/wasmtime/pull/7969)

Source published

9 Oct 2024 19:14:35 UTC

Source modified

10 Sep 2026 03:50:19 UTC

Observed here

24 Oct 2026 13:19:54 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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 · 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:L/AC:H/PR:H/UI:R/S:U/C:N/I:L/A:L

CVSS_V4 · CVSS:4.0/AV:L/AC:L/AT:P/PR:H/UI:A/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N

Publisher rating · LOW

This is an entry in the RustSec database for the Wasmtime security advisory located at https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-7qmx-3fpx-r45m. For more information see the GitHub-hosted security advisory.

Source published

3 Oct 2024 12:00:00 UTC

Source modified

12 Oct 2026 18:00:07 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.

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