CVE-2026-34941: CWE-125: Out-of-bounds Read in bytecodealliance wasmtime
Wasmtime is a runtime for WebAssembly. Prior to 24.0.7, 36.0.7, 42.0.2, and 43.0.1, Wasmtime contains a vulnerability where when transcoding a UTF-16 string to the latin1+utf16 component-model encoding it would incorrectly validate the byte length of the input string when performing a bounds check. Specifically the number of code units were checked instead of the byte length, which is twice the size of the code units. This vulnerability can cause the host to read beyond the end of a WebAssembly's linear memory in an attempt to transcode nonexistent bytes. In Wasmtime's default configuration this will read unmapped memory on a guard page, terminating the process with a segfault. Wasmtime can be configured, however, without guard pages which would mean that host memory beyond the end of linear memory may be read and interpreted as UTF-16. A host segfault is a denial-of-service vulnerability in Wasmtime, and possibly being able to read beyond the end of linear memory is additionally a vulnerability. Note that reading beyond the end of linear memory requires nonstandard configuration of Wasmtime, specifically with guard pages disabled. This vulnerability is fixed in 24.0.7, 36.0.7, 42.0.2, and 43.0.1.
AI Analysis
Technical Summary
Wasmtime versions before 24.0.7, 36.0.7, 42.0.2, and 43.0.1 contain a vulnerability (CWE-125) where UTF-16 to latin1+utf16 component-model encoding transcoding incorrectly validates input length by code units rather than bytes. This leads to an out-of-bounds read beyond the WebAssembly linear memory. In default configurations with guard pages, this causes a host process segfault (denial-of-service). Without guard pages, it may read host memory beyond linear memory, potentially exposing unintended data. The vulnerability is fixed in the specified versions. The CVSS 4.0 score is 6.9 (medium severity). No vendor advisory or patch links are provided; patch status is not explicitly confirmed.
Potential Impact
The primary impact is a denial-of-service via host process crash due to out-of-bounds memory read during string transcoding. In nonstandard configurations without guard pages, there is an additional risk of reading host memory beyond the intended bounds, which could lead to information disclosure. No known exploits are reported in the wild.
Mitigation Recommendations
Fixed versions 24.0.7, 36.0.7, 42.0.2, and 43.0.1 address this vulnerability. Since no explicit vendor advisory or patch links are provided, users should upgrade to these or later versions to remediate the issue. Default Wasmtime configurations with guard pages mitigate the risk of memory disclosure by causing a segfault instead. Users should verify their Wasmtime configuration and apply updates accordingly. Patch status is not yet confirmed by vendor advisory; check official bytecodealliance sources for current remediation guidance.
CVE-2026-34941: CWE-125: Out-of-bounds Read in bytecodealliance wasmtime
Description
Wasmtime is a runtime for WebAssembly. Prior to 24.0.7, 36.0.7, 42.0.2, and 43.0.1, Wasmtime contains a vulnerability where when transcoding a UTF-16 string to the latin1+utf16 component-model encoding it would incorrectly validate the byte length of the input string when performing a bounds check. Specifically the number of code units were checked instead of the byte length, which is twice the size of the code units. This vulnerability can cause the host to read beyond the end of a WebAssembly's linear memory in an attempt to transcode nonexistent bytes. In Wasmtime's default configuration this will read unmapped memory on a guard page, terminating the process with a segfault. Wasmtime can be configured, however, without guard pages which would mean that host memory beyond the end of linear memory may be read and interpreted as UTF-16. A host segfault is a denial-of-service vulnerability in Wasmtime, and possibly being able to read beyond the end of linear memory is additionally a vulnerability. Note that reading beyond the end of linear memory requires nonstandard configuration of Wasmtime, specifically with guard pages disabled. This vulnerability is fixed in 24.0.7, 36.0.7, 42.0.2, and 43.0.1.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
Wasmtime versions before 24.0.7, 36.0.7, 42.0.2, and 43.0.1 contain a vulnerability (CWE-125) where UTF-16 to latin1+utf16 component-model encoding transcoding incorrectly validates input length by code units rather than bytes. This leads to an out-of-bounds read beyond the WebAssembly linear memory. In default configurations with guard pages, this causes a host process segfault (denial-of-service). Without guard pages, it may read host memory beyond linear memory, potentially exposing unintended data. The vulnerability is fixed in the specified versions. The CVSS 4.0 score is 6.9 (medium severity). No vendor advisory or patch links are provided; patch status is not explicitly confirmed.
Potential Impact
The primary impact is a denial-of-service via host process crash due to out-of-bounds memory read during string transcoding. In nonstandard configurations without guard pages, there is an additional risk of reading host memory beyond the intended bounds, which could lead to information disclosure. No known exploits are reported in the wild.
Mitigation Recommendations
Fixed versions 24.0.7, 36.0.7, 42.0.2, and 43.0.1 address this vulnerability. Since no explicit vendor advisory or patch links are provided, users should upgrade to these or later versions to remediate the issue. Default Wasmtime configurations with guard pages mitigate the risk of memory disclosure by causing a segfault instead. Users should verify their Wasmtime configuration and apply updates accordingly. Patch status is not yet confirmed by vendor advisory; check official bytecodealliance sources for current remediation guidance.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-03-31T17:27:08.660Z
- Cvss Version
- 4.0
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 69d843791cc7ad14da3fb68c
Added to database: 4/10/2026, 12:25:29 AM
Last enriched: 4/17/2026, 12:24:54 PM
Last updated: 5/25/2026, 7:37:16 AM
Views: 121
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