CVE-2026-35186: CWE-789: Memory Allocation with Excessive Size Value in bytecodealliance wasmtime
Wasmtime is a runtime for WebAssembly. From 25.0.0 to before 36.0.7, 42.0.2, and 43.0.1, Wasmtime's Winch compiler backend contains a bug where translating the table.grow operator causes the result to be incorrectly typed. For 32-bit tables this means that the result of the operator, internally in Winch, is tagged as a 64-bit value instead of a 32-bit value. This invalid internal representation of Winch's compiler state compounds into further issues depending on how the value is consumed. The primary consequence of this bug is that bytes in the host's address space can be stored/read from. This is only applicable to the 16 bytes before linear memory, however, as the only significant return value of table.grow that can be misinterpreted is -1. The bytes before linear memory are, by default, unmapped memory. Wasmtime will detect this fault and abort the process, however, because wasm should not be able to access these bytes. Overall this this bug in Winch represents a DoS vector by crashing the host process, a correctness issue within Winch, and a possible leak of up to 16-bytes before linear memory. Wasmtime's default compiler is Cranelift, not Winch, and Wasmtime's default settings are to place guard pages before linear memory. This means that Wasmtime's default configuration is not affected by this issue, and when explicitly choosing Winch Wasmtime's otherwise default configuration leads to a DoS. Disabling guard pages before linear memory is required to possibly leak up to 16-bytes of host data. This vulnerability is fixed in 36.0.7, 42.0.2, and 43.0.1.
AI Analysis
Technical Summary
Wasmtime's Winch compiler backend incorrectly types the result of the table.grow operator for 32-bit tables, tagging it as a 64-bit value instead of 32-bit. This internal misrepresentation can cause the host process to crash (DoS) and potentially leak up to 16 bytes of host memory located before linear memory if guard pages are disabled. The default Wasmtime configuration, which uses the Cranelift compiler and guard pages, is not affected. The vulnerability affects multiple Wasmtime version ranges and is fixed in versions 36.0.7, 42.0.2, and 43.0.1.
Potential Impact
The vulnerability can cause denial-of-service by crashing the host process due to invalid memory access. Additionally, if guard pages before linear memory are disabled, there is a potential for leaking up to 16 bytes of host memory. The default Wasmtime configuration is not affected, limiting the impact to environments explicitly using the Winch compiler backend with disabled guard pages.
Mitigation Recommendations
Upgrading Wasmtime to versions 36.0.7, 42.0.2, or 43.0.1 or later resolves this vulnerability. Users should ensure that the default Cranelift compiler and guard pages before linear memory remain enabled to avoid exposure. If using the Winch compiler backend, it is critical to apply the fixed versions to prevent denial-of-service and potential memory leakage. Patch status is not explicitly confirmed in the input data, but the vendor-provided fixed versions indicate an official fix is available.
CVE-2026-35186: CWE-789: Memory Allocation with Excessive Size Value in bytecodealliance wasmtime
Description
Wasmtime is a runtime for WebAssembly. From 25.0.0 to before 36.0.7, 42.0.2, and 43.0.1, Wasmtime's Winch compiler backend contains a bug where translating the table.grow operator causes the result to be incorrectly typed. For 32-bit tables this means that the result of the operator, internally in Winch, is tagged as a 64-bit value instead of a 32-bit value. This invalid internal representation of Winch's compiler state compounds into further issues depending on how the value is consumed. The primary consequence of this bug is that bytes in the host's address space can be stored/read from. This is only applicable to the 16 bytes before linear memory, however, as the only significant return value of table.grow that can be misinterpreted is -1. The bytes before linear memory are, by default, unmapped memory. Wasmtime will detect this fault and abort the process, however, because wasm should not be able to access these bytes. Overall this this bug in Winch represents a DoS vector by crashing the host process, a correctness issue within Winch, and a possible leak of up to 16-bytes before linear memory. Wasmtime's default compiler is Cranelift, not Winch, and Wasmtime's default settings are to place guard pages before linear memory. This means that Wasmtime's default configuration is not affected by this issue, and when explicitly choosing Winch Wasmtime's otherwise default configuration leads to a DoS. Disabling guard pages before linear memory is required to possibly leak up to 16-bytes of host data. This vulnerability is fixed in 36.0.7, 42.0.2, and 43.0.1.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
Wasmtime's Winch compiler backend incorrectly types the result of the table.grow operator for 32-bit tables, tagging it as a 64-bit value instead of 32-bit. This internal misrepresentation can cause the host process to crash (DoS) and potentially leak up to 16 bytes of host memory located before linear memory if guard pages are disabled. The default Wasmtime configuration, which uses the Cranelift compiler and guard pages, is not affected. The vulnerability affects multiple Wasmtime version ranges and is fixed in versions 36.0.7, 42.0.2, and 43.0.1.
Potential Impact
The vulnerability can cause denial-of-service by crashing the host process due to invalid memory access. Additionally, if guard pages before linear memory are disabled, there is a potential for leaking up to 16 bytes of host memory. The default Wasmtime configuration is not affected, limiting the impact to environments explicitly using the Winch compiler backend with disabled guard pages.
Mitigation Recommendations
Upgrading Wasmtime to versions 36.0.7, 42.0.2, or 43.0.1 or later resolves this vulnerability. Users should ensure that the default Cranelift compiler and guard pages before linear memory remain enabled to avoid exposure. If using the Winch compiler backend, it is critical to apply the fixed versions to prevent denial-of-service and potential memory leakage. Patch status is not explicitly confirmed in the input data, but the vendor-provided fixed versions indicate an official fix is available.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-04-01T17:26:21.134Z
- Cvss Version
- 4.0
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 69d7f88c1cc7ad14da0c170c
Added to database: 4/9/2026, 7:05:48 PM
Last enriched: 4/17/2026, 11:52:45 AM
Last updated: 5/25/2026, 2:40:50 AM
Views: 73
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