CVE-2026-115384: Wasmtime 39.0.0 before 48.0.4 and 49.0.0 before 49.0.2 Stack Buffer Overflow
SSVC · Estimated by CveMateTrack*Monitor closely. May escalate on new signals. CISA has no entry yet, so CveMate computed this from CVSS and exploit data. It is replaced when CISA publishes.
ExploitationNone (derived)
AutomatableNo (derived)
Technical impactTotal (derived)
Mission & well-beingHigh (assumed)
Source: CveMate estimate, same decision tree as CISA.CISA publishes the first three inputs. Mission & well-being depends on your environment, so it is assumed at its highest: the decision is a worst case.
Published 22-10-2026Last modified 22-10-2026
Vulnerability summary
CVE-2026-115384 is a critical (CVSS 9.9) Improper Input Validation vulnerability in bytecodealliance wasmtime.
Overall risk
70/100
0100
High · default modelHow is this calculated?SSVC · Estimated by CveMateTrack*Monitor closely. May escalate on new signals. CISA has no entry yet, so CveMate computed this from CVSS and exploit data. It is replaced when CISA publishes.
ExploitationNone (derived)
AutomatableNo (derived)
Technical impactTotal (derived)
Mission & well-beingHigh (assumed)
Source: CveMate estimate, same decision tree as CISA.CISA publishes the first three inputs. Mission & well-being depends on your environment, so it is assumed at its highest: the decision is a worst case.
CVSS score
9.9/10
010
Critical · v3.1 (CVE.org)EPSS scoreNot scoredRisk metrics not yet published.
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits0No public exploits recorded
Timeline
- 22-10-2026PublishedVulnerability first disclosed.
Description
Wasmtime 39.0.0 before 48.0.4 and 49.0.0 before 49.0.2 contains a stack buffer overflow vulnerability that allows malicious guests to write ~16KB to the native stack via unvalidated async callback result types. Attackers can supply components with mistyped component-model-async callback functions to overwrite return addresses, crashing the host or escaping the sandbox.
CVSS metrics
4 scores · 2 sources · 2 versionsCritical 9.4Preferred score · CVE.org (CNA)
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:HSourcesAll 2 agree
- NVDNIST9.4CriticalCVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Critical 9.9Preferred score · CVE.org (CNA)
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:HSourcesAll 2 agree
- NVDNIST9.9CriticalCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
EPSS trend
No EPSS score has been published for this record yet.
Known exploited
Compare KEV catalogs
CISA KEVNot in the CISA KEV catalog.
ENISA CNWNot in the ENISA CNW catalog.
CIRCLNot in the CIRCL catalog.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeAffected systems
Bytecodealliance1 product
- wasmtime≥ 39.0.0, < 48.0.4 | ≥ 49.0.0, < 49.0.2
1 vendor · 1 product
References
2 links- www.vulncheck.com/advisories/…Third Party Advisory
Related vulnerabilities
MediumCVE-2021-39218bytecodealliance · wasmtimeOut-of-bounds read/write and invalid free with `externref`s and GC safepoints in WasmtimeWasmtime 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`.EPSS0.30%MediumCVE-2021-39216bytecodealliance · wasmtime +3 moreUse after free passing `externref`s to Wasm in WasmtimeWasmtime 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`.EPSS0.31%MediumCVE-2021-39219bytecodealliance · wasmtimeWrong type for `Linker`-define functions when used across two `Engine`sWasmtime is an open source runtime for WebAssembly & WASI. Wasmtime before version 0.30.0 is affected by a type confusion vulnerability. As a Rust library the `wasmtime` crate clearly marks which functions are safe and which are `unsafe`, guaranteeing that if consumers never use `unsafe` then it should not be possible to have memory unsafety issues in their embeddings of Wasmtime. An issue was discovered in the safe API of `Linker::func_*` APIs. These APIs were previously not sound when one `Engine` was used to create the `Linker` and then a different `Engine` was used to create a `Store` and then the `Linker` was used to instantiate a module into that `Store`. Cross-`Engine` usage of functions is not supported in Wasmtime and this can result in type confusion of function pointers, resulting in being able to safely call a function with the wrong type. Triggering this bug requires using at least two `Engine` values in an embedding and then additionally using two different values with a `Linker` (one at the creation time of the `Linker` and another when instantiating a module with the `Linker`). It's expected that usage of more-than-one `Engine` in an embedding is relatively rare since an `Engine` is intended to be a globally shared resource, so the expectation is that the impact of this issue is relatively small. The fix implemented is to change this behavior to `panic!()` in Rust instead of silently allowing it. Using different `Engine` instances with a `Linker` is a programmer bug that `wasmtime` catches at runtime. This bug has been patched and users should upgrade to Wasmtime version 0.30.0. If you cannot upgrade Wasmtime and are using more than one `Engine` in your embedding it's recommended to instead use only one `Engine` for the entire program if possible. An `Engine` is designed to be a globally shared resource that is suitable to have only one for the lifetime of an entire process. If using multiple `Engine`s is required then code should be audited to ensure that `Linker` is only used with one `Engine`.EPSS0.36%HighCVE-2021-32629bytecodealliance · cranelift-codegen +4 moreMemory access due to code generation flaw in Cranelift moduleCranelift is an open-source code generator maintained by Bytecode Alliance. It translates a target-independent intermediate representation into executable machine code. There is a bug in 0.73 of the Cranelift x64 backend that can create a scenario that could result in a potential sandbox escape in a Wasm program. This bug was introduced in the new backend on 2020-09-08 and first included in a release on 2020-09-30, but the new backend was not the default prior to 0.73. The recently-released version 0.73 with default settings, and prior versions with an explicit build flag to select the new backend, are vulnerable. The bug in question performs a sign-extend instead of a zero-extend on a value loaded from the stack, under a specific set of circumstances. If those circumstances occur, the bug could allow access to memory addresses upto 2GiB before the start of the Wasm program heap. If the heap bound is larger than 2GiB, then it would be possible to read memory from a computable range dependent on the size of the heaps bound. The impact of this bug is highly dependent on heap implementation, specifically: * if the heap has bounds checks, and * does not rely exclusively on guard pages, and * the heap bound is 2GiB or smaller * then this bug cannot be used to reach memory from another Wasm program heap. The impact of the vulnerability is mitigated if there is no memory mapped in the range accessible using this bug, for example, if there is a 2 GiB guard region before the Wasm program heap. The bug in question performs a sign-extend instead of a zero-extend on a value loaded from the stack, when the register allocator reloads a spilled integer value narrower than 64 bits. This interacts poorly with another optimization: the instruction selector elides a 32-to-64-bit zero-extend operator when we know that an instruction producing a 32-bit value actually zeros the upper 32 bits of its destination register. Hence, we rely on these zeroed bits, but the type of the value is still i32, and the spill/reload reconstitutes those bits as the sign extension of the i32’s MSB. The issue would thus occur when: * An i32 value in a Wasm program is greater than or equal to 0x8000_0000; * The value is spilled and reloaded by the register allocator due to high register pressure in the program between the value’s definition and its use; * The value is produced by an instruction that we know to be “special” in that it zeroes the upper 32 bits of its destination: add, sub, mul, and, or; * The value is then zero-extended to 64 bits in the Wasm program; * The resulting 64-bit value is used. Under these circumstances there is a potential sandbox escape when the i32 value is a pointer. The usual code emitted for heap accesses zero-extends the Wasm heap address, adds it to a 64-bit heap base, and accesses the resulting address. If the zero-extend becomes a sign-extend, the program could reach backward and access memory up to 2GiB before the start of its heap. In addition to assessing the nature of the code generation bug in Cranelift, we have also determined that under specific circumstances, both Lucet and Wasmtime using this version of Cranelift may be exploitable. See referenced GitHub Advisory for more details.EPSS0.46%LowCVE-2025-61670bytecodealliance · wasmtime +2 moreWasmtime has memory leak in C API with `externref` and `anyref` typesWasmtime is a runtime for WebAssembly. Wasmtime 37.0.0 and 37.0.1 have memory leaks in the C/C++ API when using bindings for the `anyref` or `externref` WebAssembly values. This is caused by a regression introduced during the development of 37.0.0 and all prior versions of Wasmtime are unaffected. If `anyref` or `externref` is not used in the C/C++ API then embeddings are also unaffected by the leaky behavior. The `wasmtime` Rust crate is unaffected by this leak.
Development of Wasmtime 37.0.0 included a refactoring in Rust of changing the old `ManuallyRooted<T>` type to a new `OwnedRooted<T>` type. This change was integrated into Wasmtime's C API but left the C API in a state which had memory leaks. Additionally the new ownership semantics around this type were not reflected into the C++ API, making it leak-prone. A short version of the change is that previously `ManuallyRooted<T>`, as the name implies, required manual calls to an "unroot" operation. If this was forgotten then the memory was still cleaned up when the `wasmtime_store_t` itself was destroyed eventually. Documentation of when to "unroot" was sparse and there were already situations prior to 37.0.0 where memory would be leaked until the store was destroyed anyway. All memory, though, was always bound by the store, and destroying the store would guarantee that there were no memory leaks.
In migrating to `OwnedRooted<T>` the usage of the type in Rust changed. A manual "unroot" operation is no longer required and it happens naturally as a destructor of the `OwnedRooted<T>` type in Rust itself. These new resource ownership semantics were not fully integrated into the preexisting semantics of the C/C++ APIs in Wasmtime. A crucial distinction of `OwnedRooted<T>` vs `ManuallyRooted<T>` is that the `OwnedRooted<T>` type allocates host memory outside of the store. This means that if an `OwnedRooted<T>` is leaked then destroying a store does not release this memory and it's a permanent memory leak on the host.
This led to a few distinct, but related, issues arising: A typo in the `wasmtime_val_unroot` function in the C API meant that it did not actually unroot anything. This meant that even if embedders faithfully call the function then memory will be leaked. If a host-defined function returned a `wasmtime_{externref,anyref}_t` value then the value was never unrooted. The C/C++ API no longer has access to the value and the Rust implementation did not unroot. This meant that any values returned this way were never unrooted. The goal of the C++ API of Wasmtime is to encode automatic memory management in the type system, but the C++ API was not updated when `OwnedRooted<T>` was added. This meant that idiomatic usage of the C++ API would leak memory due to a lack of destructors on values.
These issues have all been fixed in a 37.0.2 release of Wasmtime. The implementation of the C and C++ APIs have been updated accordingly and respectively to account for the changes of ownership here. For example `wasmtime_val_unroot` has been fixed to unroot, the Rust-side implementation of calling an embedder-defined function will unroot return values, and the C++ API now has destructors on the `ExternRef`, `AnyRef`, and `Val` types. These changes have been made to the 37.0.x release branch in a non-API-breaking fashion. Changes to the 38.0.0 release branch (and `main` in the Wasmtime repository) include minor API updates to better accommodate the API semantic changes. The only known workaround at this time is to avoid using `externref` and `anyref` in the C/C++ API of Wasmtime. If avoiding those types is not possible then it's required for users to update to mitigate the leak issue.EPSS0.19%LowCVE-2025-62711bytecodealliance · wasmtime +2 moreWasmtime vulnerable to segfault when using component resourcesWasmtime is a runtime for WebAssembly. In versions from 38.0.0 to before 38.0.3, the implementation of component-model related host-to-wasm trampolines in Wasmtime contained a bug where it's possible to carefully craft a component, which when called in a specific way, would crash the host with a segfault or assert failure. Wasmtime 38.0.3 has been released and is patched to fix this issue. There are no workarounds.EPSS0.43%
All vulnerabilities inwasmtime