CVE-2026-115889
Wasmtime: Bit-packing in Cranelift compiler causes silent overflow and miscompilation
Wasmtime is a runtime for WebAssembly. Prior to 36.0.19 and 43.0.0, the Cranelift compiler backend bit-packs SSA value indices in a way that can silently overflow in release builds when compiling a sufficiently large or specially crafted Wasm function with many SSA values. The overflow can make Cranelift reference incorrect IR values, causing arbitrary miscompilation, type confusion, and other attacker-controlled effects that may escape the Wasm sandbox on any architecture using the default Cranelift backend. This issue is fixed in versions 36.0.19 and 43.0.0.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- Low
- User interaction
- None
What an attacker can affect
- Confidentiality
- High
- Integrity
- High
- Availability
- High
Exploit likelihood
What each source reports
CVE List Score used
Wasmtime: Bit-packing in Cranelift compiler causes silent overflow and miscompilation
Wasmtime is a runtime for WebAssembly. Prior to 36.0.19 and 43.0.0, the Cranelift compiler backend bit-packs SSA value indices in a way that can silently overflow in release builds when compiling a sufficiently large or specially crafted Wasm function with many SSA values. The overflow can make Cranelift reference incorrect IR values, causing arbitrary miscompilation, type confusion, and other attacker-controlled effects that may escape the Wasm sandbox on any architecture using the default Cranelift backend. This issue is fixed in versions 36.0.19 and 43.0.0.
- Record
CVE-2026-115889- CVSS 3.1
- 9.9 Critical
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H - Weakness
- CWE-197, CWE-843
- Updated
- 2026-11-02
EUVDEUVD-2026-109186
Wasmtime is a runtime for WebAssembly. Prior to 36.0.19 and 43.0.0, the Cranelift compiler backend bit-packs SSA value indices in a way that can silently overflow in release builds when compiling a sufficiently large or specially crafted Wasm function with many SSA values. The overflow can make Cranelift reference incorrect IR values, causing arbitrary miscompilation, type confusion, and other attacker-controlled effects that may escape the Wasm sandbox on any architecture using the default Cranelift backend. This issue is fixed in versions 36.0.19 and 43.0.0.
- Record
EUVD-2026-109186- CVSS 3.1
- 9.9 Critical
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H - Updated
- 2026-11-02
GitHub AdvisoriesGHSA-897f-g5gm-fmxm
Wasmtime: Bit-packing in Cranelift compiler causes silent overflow and miscompilation
Summary
In Wasmtime prior to v43, the Cranelift compiler backend bit-packs its SSA value indices in a way that can result in silent overflow in release builds, and result in incorrect value references in the IR resulting in arbitrary miscompilation. A very large Wasm function body, or one that is specially crafted to use many SSA values, can use this to force type-confusion or other arbitrary side-effects and escape the sandbox.
Cranelift was changed in Wasmtime v43 to use a full u32 index, with checks if that limit is exceeded, and so is no longer susceptible to this bug.
Impact
A Wasmtime engine with default settings (using the Cranelift backend) on any architecture/platform could experience a sandbox escape from a specially-crafted Wasm module.
Patches
Wasmtime v36.0.19 has been released which fixes this issue.
- Record
GHSA-897f-g5gm-fmxm- CVSS 3.1
- 9.9 Critical
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H - Weakness
- CWE-197, CWE-843
- Updated
- 2026-11-02
NVD
Wasmtime is a runtime for WebAssembly. Prior to 36.0.19 and 43.0.0, the Cranelift compiler backend bit-packs SSA value indices in a way that can silently overflow in release builds when compiling a sufficiently large or specially crafted Wasm function with many SSA values. The overflow can make Cranelift reference incorrect IR values, causing arbitrary miscompilation, type confusion, and other attacker-controlled effects that may escape the Wasm sandbox on any architecture using the default Cranelift backend. This issue is fixed in versions 36.0.19 and 43.0.0.
- Record
CVE-2026-115889- CVSS 3.1
- 9.9 Critical
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H - Weakness
- CWE-197, CWE-843
- Updated
- 2026-11-02
OSV
Wasmtime: Bit-packing in Cranelift compiler causes silent overflow and miscompilation
Wasmtime is a runtime for WebAssembly. Prior to 36.0.19 and 43.0.0, the Cranelift compiler backend bit-packs SSA value indices in a way that can silently overflow in release builds when compiling a sufficiently large or specially crafted Wasm function with many SSA values. The overflow can make Cranelift reference incorrect IR values, causing arbitrary miscompilation, type confusion, and other attacker-controlled effects that may escape the Wasm sandbox on any architecture using the default Cranelift backend. This issue is fixed in versions 36.0.19 and 43.0.0.
- Record
CVE-2026-115889- CVSS 3.1
- 9.9 Critical
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H - Weakness
- CWE-197, CWE-843
- Updated
- 2026-11-02
OSVDEBIAN-CVE-2026-115889
Wasmtime is a runtime for WebAssembly. Prior to 36.0.19 and 43.0.0, the Cranelift compiler backend bit-packs SSA value indices in a way that can silently overflow in release builds when compiling a sufficiently large or specially crafted Wasm function with many SSA values. The overflow can make Cranelift reference incorrect IR values, causing arbitrary miscompilation, type confusion, and other attacker-controlled effects that may escape the Wasm sandbox on any architecture using the default Cranelift backend. This issue is fixed in versions 36.0.19 and 43.0.0.
- Record
DEBIAN-CVE-2026-115889- CVSS 3.1
- 9.9 Critical
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H - Updated
- 2026-11-03
Show 5 moreShow less
OSVGHSA-897f-g5gm-fmxm
Wasmtime: Bit-packing in Cranelift compiler causes silent overflow and miscompilation
Summary
In Wasmtime prior to v43, the Cranelift compiler backend bit-packs its SSA value indices in a way that can result in silent overflow in release builds, and result in incorrect value references in the IR resulting in arbitrary miscompilation. A very large Wasm function body, or one that is specially crafted to use many SSA values, can use this to force type-confusion or other arbitrary side-effects and escape the sandbox.
Cranelift was changed in Wasmtime v43 to use a full u32 index, with checks if that limit is exceeded, and so is no longer susceptible to this bug.
Impact
A Wasmtime engine with default settings (using the Cranelift backend) on any architecture/platform could experience a sandbox escape from a specially-crafted Wasm module.
Patches
Wasmtime v36.0.19 has been released which fixes this issue.
- Record
GHSA-897f-g5gm-fmxm- CVSS 3.1
- 9.9 Critical
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H - Weakness
- CWE-197, CWE-843
- Updated
- 2026-11-02
OSVRUSTSEC-2026-0380
Bit-packing in Cranelift compiler causes silent overflow and miscompilation
This is an entry in the RustSec database for the Wasmtime security advisory located at https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-897f-g5gm-fmxm For more information see the GitHub-hosted security advisory.
- Record
RUSTSEC-2026-0380- CVSS 3.1
- 9.9 Critical
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H - Updated
- 2026-11-02
OSVUBUNTU-CVE-2026-115889
Wasmtime is a runtime for WebAssembly. Prior to 36.0.19 and 43.0.0, the Cranelift compiler backend bit-packs SSA value indices in a way that can silently overflow in release builds when compiling a sufficiently large or specially crafted Wasm function with many SSA values. The overflow can make Cranelift reference incorrect IR values, causing arbitrary miscompilation, type confusion, and other attacker-controlled effects that may escape the Wasm sandbox on any architecture using the default Cranelift backend. This issue is fixed in versions 36.0.19 and 43.0.0.
- Record
UBUNTU-CVE-2026-115889- CVSS 3.1
- 9.9 Critical
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H - Updated
- 2026-11-02
OSVAZL-111431 No score
CVE-2026-115889 affecting package rust for versions less than 1.75.0-31
Wasmtime is a runtime for WebAssembly. Prior to 36.0.19 and 43.0.0, the Cranelift compiler backend bit-packs SSA value indices in a way that can silently overflow in release builds when compiling a sufficiently large or specially crafted Wasm function with many SSA values. The overflow can make Cranelift reference incorrect IR values, causing arbitrary miscompilation, type confusion, and other attacker-controlled effects that may escape the Wasm sandbox on any architecture using the default Cranelift backend. This issue is fixed in versions 36.0.19 and 43.0.0.
- Record
AZL-111431- Updated
- 2026-11-05
OSVAZL-111437 No score
CVE-2026-115889 affecting package rust for versions less than 1.98.1-1
Wasmtime is a runtime for WebAssembly. Prior to 36.0.19 and 43.0.0, the Cranelift compiler backend bit-packs SSA value indices in a way that can silently overflow in release builds when compiling a sufficiently large or specially crafted Wasm function with many SSA values. The overflow can make Cranelift reference incorrect IR values, causing arbitrary miscompilation, type confusion, and other attacker-controlled effects that may escape the Wasm sandbox on any architecture using the default Cranelift backend. This issue is fixed in versions 36.0.19 and 43.0.0.
- Record
AZL-111437- Updated
- 2026-11-05
Affected products
Affected packages
| Package | Affected | Fixed |
|---|---|---|
wasmtimecrates.io |
before 36.0.19 | 36.0.19 |
wasmtimecrates.io |
37.0.0 up to 43.0.0 | 43.0.0 |
rustAzure Linux:3 |
before 1.75.0-31 | 1.75.0-31 |
rustAzure Linux:3 |
1.85.0 up to 1.98.1-1 | 1.98.1-1 |
rust-wasmtimeDebian:13 |
All versions, plus listed versions 26.0.1+dfsg-1026.0.1+dfsg-326.0.1+dfsg-426.0.1+dfsg-526.0.1+dfsg-6 Show 39 moreShow less26.0.1+dfsg-726.0.1+dfsg-826.0.1+dfsg-927.0.0+dfsg-227.0.0+dfsg-327.0.0+dfsg-428.0.1+dfsg-128.0.1+dfsg-228.0.1+dfsg-329.0.1+dfsg-129.0.1+dfsg-229.0.1+dfsg-329.0.1+dfsg-429.0.1+dfsg-529.0.1+dfsg-629.0.1+dfsg-729.0.1+dfsg-836.0.11+dfsg-136.0.12+dfsg-136.0.12+dfsg-236.0.12+dfsg-336.0.13+dfsg-136.0.20+dfsg-136.0.5+dfsg-136.0.5+dfsg-236.0.5+dfsg-336.0.5+dfsg-436.0.5+dfsg-536.0.6+dfsg-136.0.6+dfsg-236.0.6+dfsg-336.0.6+dfsg-436.0.6+dfsg-536.0.6+dfsg-636.0.6+dfsg-736.0.7+dfsg-136.0.8+dfsg-136.0.9+dfsg-136.0.9+dfsg-2 |
None known |
rust-wasmtimeDebian:14 |
before 36.0.20+dfsg-1, plus listed versions 26.0.1+dfsg-1026.0.1+dfsg-326.0.1+dfsg-426.0.1+dfsg-526.0.1+dfsg-6 Show 38 moreShow less26.0.1+dfsg-726.0.1+dfsg-826.0.1+dfsg-927.0.0+dfsg-227.0.0+dfsg-327.0.0+dfsg-428.0.1+dfsg-128.0.1+dfsg-228.0.1+dfsg-329.0.1+dfsg-129.0.1+dfsg-229.0.1+dfsg-329.0.1+dfsg-429.0.1+dfsg-529.0.1+dfsg-629.0.1+dfsg-729.0.1+dfsg-836.0.11+dfsg-136.0.12+dfsg-136.0.12+dfsg-236.0.12+dfsg-336.0.13+dfsg-136.0.5+dfsg-136.0.5+dfsg-236.0.5+dfsg-336.0.5+dfsg-436.0.5+dfsg-536.0.6+dfsg-136.0.6+dfsg-236.0.6+dfsg-336.0.6+dfsg-436.0.6+dfsg-536.0.6+dfsg-636.0.6+dfsg-736.0.7+dfsg-136.0.8+dfsg-136.0.9+dfsg-136.0.9+dfsg-2 |
36.0.20+dfsg-1 |
wasmtimecrates.io |
0.0.0-0 up to 36.0.19, 37.0.0 up to 43.0.0 | 36.0.1943.0.0 |
rust-wasmtimeUbuntu:24.04:LTS |
All versions, plus listed versions 10.0.1+dfsg-715.0.1+dfsg-416.0.0+dfsg-216.0.0+dfsg-3 |
None known |
rust-wasmtimeUbuntu:26.10 |
All versions, plus listed versions 36.0.5+dfsg-136.0.13+dfsg-1 |
None known |
rust-wasmtimeUbuntu:26.04:LTS |
All versions, plus listed versions 26.0.1+dfsg-326.0.1+dfsg-428.0.1+dfsg-329.0.1+dfsg-536.0.5+dfsg-1 |
None known |
Public exploits
Links only. Every CVE stores no exploit code.
| Source | Link | Date |
|---|---|---|
| PoC in GitHub | ideator-labs/wasmtime-sweep | 2026-10-27 |
History
| Recorded | Changed | Sources |
|---|---|---|
| affected, facts | OSV | |
| affected | OSV | |
| first indexed | CVE List, EUVD, GitHub Advisories, NVD, OSV, PoC in GitHub |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2026-115889 is a critical vulnerability (CVSS 9.9) in Bytecodealliance Wasmtime, published October 19, 2026. Public exploit code exists. EPSS puts the chance of exploitation in the next 30 days at 0.45%, the 39th percentile. Fixed in wasmtime 36.0.19.
References
github.com/bytecodealliance/wasmtime/security/advisories/GHSA-897f-g5gm-fmxm
Show 10 moreShow less
rustsec.org/advisories/RUSTSEC-2026-0380.html
nvd.nist.gov/vuln/detail/CVE-2026-115889
security-tracker.debian.org/tracker/CVE-2026-115889
crates.io/crates/wasmtime
ubuntu.com/security/CVE-2026-115889
cve.org/CVERecord?id=CVE-2026-115889