Wasmtime has a use-after-free bug after cloning `wasmtime::Linker`
Key facts
- Attack vector
- Physical
- Privileges required
- High
- User interaction
- Active
- Attack complexity
- High
- Attack requirements
- Present
- Impact type
- —
- Confidentiality · integrity · availability
- Low · Low · Low
- Fix status
- Partial Red Hat: 2 without a fix
Attack profile from CVSS 4.0 · CNA. Fix status from CNA, GitHub and Red Hat.
Summary
Wasmtime is a runtime for WebAssembly. In 43.0.0, cloning a wasmtime::Linker is unsound and can result in use-after-free bugs. This bug is not controllable by guest Wasm programs. It can only be triggered by a specific sequence of embedder API calls made by the host. Specifically, the following steps must occur to trigger the bug clone a wasmtime::Linker, drop the original linker instance, use the new, cloned linker instance, resulting in a use-after-free. This vulnerability is fixed in 43.0.1.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- Poc
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| bytecodealliance | wasmtime | 43.0.0 to before 43.0.1 | 43.0.1 | Patch available | CNA |
| — | wasmtime (crates.io) | 43.0.0 to before 43.0.1 | 43.0.1 | Patch available | GHSA-hfr4-7c6c-48w2 |
- wasmtime Vendorbytecodealliance Affected 43.0.0 to before 43.0.1 Fixed in 43.0.1 Patch available CNA
- wasmtime (crates.io) Vendor— Affected 43.0.0 to before 43.0.1 Fixed in 43.0.1 Patch available GHSA-hfr4-7c6c-48w2
CPE configurations NVD · 1
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:bytecodealliance:wasmtime:43.0.0:*:*:*:*:rust:*:* | 43.0.0 | Vulnerable | bytecodealliance |
- cpe:2.3:a:bytecodealliance:wasmtime:43.0.0:*:*:*:*:rust:*:* Versions 43.0.0 Vulnerable ·bytecodealliance
Remediation
- Fix · CNA wasmtime (bytecodealliance) Fixed in 43.0.1
- Fix · GHSA-hfr4-7c6c-48w2 wasmtime (crates.io) Fixed in 43.0.1 Advisory →
Vendor assessments
Red Hat
Red Hat rating: Low. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Connectivity Link 1 | Affected | No fix yet: Fix deferred |
| Red Hat Enterprise Linux 10 | Affected | No fix yet: Fix deferred |
Timeline
- 2026-10-02 Threatist record created from CVE-2026-34983
- 2026-10-03 Alias added: GHSA-hfr4-7c6c-48w2
References
Advisory 2
More bytecodealliance Wasmtime vulnerabilities
- TI-2026-21632 Wasmtime is vulnerable to panic when dropping a `[Typed]Func::call_async` future CVSS 4.0MEDIUM 6.9
- TI-2023-11636 Guest-controlled out-of-bounds read/write on x86_64 in wasmtime CVSS 3.1CRITICAL 10.0
- TI-2022-18765 Wasmtime vulnerable to data leakage between instances in the pooling allocator CVSS 3.1HIGH 8.6
- TI-2022-08604 Use after free in Wasmtime CVSS 3.1CRITICAL 9.8
- TI-2022-18766 wasmtime_trap_code C API function has out of bounds write vulnerability CVSS 3.1CRITICAL 9.8
- TI-2026-27209 Wasmtime with Winch compiler backend on aarch64 may allow a sandbox-escaping memory access CVSS 4.0CRITICAL 9.0
Sources
- CVE-2026-34983 · CVE Program
- CVE-2026-34983 · NVD
- FIRST EPSS
- GHSA-hfr4-7c6c-48w2 · GitHub Advisory Database · CC BY 4.0
- CVE-2026-34983 · Red Hat security data · CC BY 4.0
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