Wasmtime: Sandbox escape via incorrect branch target in aarch64 Cranelift br_table
Summary
Wasmtime's Cranelift compiler backend on aarch64 (ARM64) can generate an incorrect conditional branch target when compiling a WebAssembly br_table instruction with more than about 256,000 targets. An attacker who can supply a Wasm module to such a host can jump to arbitrary code at a user-controlled offset and escape the Wasm sandbox. Exploitation requires that the host runs untrusted or user-supplied Wasm modules on ARM64 with the default Cranelift backend.
Affected
- Wasmtime before 36.0.19
- Wasmtime 37.0.0 before 48.0.7
- Wasmtime 49.0.0 before 49.0.4
- Only aarch64 (ARM64) hosts using the default Cranelift backend are affected; x86-64 is not affected according to the research notes
- Unknown: whether older releases that support aarch64 are affected, as some secondary sources state
Fixed in
- Wasmtime 36.0.19
- Wasmtime 48.0.7
- Wasmtime 49.0.4
Workaround
Unknown.
- No vendor-published workaround found.
- Until patched, run only trusted Wasm modules on ARM64 hosts and move untrusted-module workloads to x86-64 hosts.
Exploitation
- Vendor advisory and news coverage report no known exploitation as of October 26, 2026.
- CISA SSVC assessment: exploitation none, not automatable.
- CISA KEV: not listed in the latest checks found.
- A public GitHub repository claims a working exploit; this is unverified and may be fake or malicious. Do not run code from it.
Our recommendation
- Inventory all Wasmtime copies, including embedded copies in third-party software and containers, and identify ARM64 hosts.
- Update Wasmtime to 36.0.19, 48.0.7 or 49.0.4, or move to a supported release line that includes the fix.
- Until patched, restrict Wasm execution on ARM64 hosts to trusted modules.
- Ask software vendors that embed Wasmtime for their patch status.
- Do not run code from unverified public exploit repositories.
Public exploits
Links to third-party sites, not checked by us – exploit code can contain malware. Only use it in isolated test environments.
- Proof of concept on GitHub (1 repositories)
shreyas-malhotra/CVE-2026-115893-wasmtime-sandbox-escape
Research sources
- GHSA-mghf-wjfp-p5xm security advisory github.com
- Wasmtime release 36.0.19 github.com
- Wasmtime release 48.0.7 github.com
- Wasmtime release 49.0.4 github.com
- Wasmtime fix commit 222ff3a github.com
- OSV record GHSA-mghf-wjfp-p5xm osv.dev
- The Hacker News: Two critical Wasmtime flaws thehackernews.com
- Ubuntu CVE-2026-115893 ubuntu.com
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 30 Oct 2026, 14:56.
Original description (NVD)
Wasmtime is a runtime for WebAssembly. Prior to 36.0.19, 48.0.7, and 49.0.4, the Cranelift compiler backend on aarch64 can compile a Wasm br_table instruction with more than approximately 256,000 targets so that it has an incorrect conditional branch target. The branch can then jump to arbitrary other code at a user-controlled offset, allowing a user-controlled Wasm module to escape the sandbox on aarch64 engines using the default Cranelift backend. This issue is fixed in versions 36.0.19, 48.0.7, and 49.0.4.
NVD references (12)
- https://github.com/bytecodealliance/wasmtime/commit/222ff3a65dab9aa7011f8c246937751a0bac5abd
- https://github.com/bytecodealliance/wasmtime/commit/994549891c8a706cb4f2809f9d17b9f67b31e618
- https://github.com/bytecodealliance/wasmtime/commit/e61df1b454be9313d61a5f8de07722a421139bbe
- https://github.com/bytecodealliance/wasmtime/commit/f517bd6e890c7c1291ab9fe05d8cc0c9f11e56aa
- https://github.com/bytecodealliance/wasmtime/pull/14818
- https://github.com/bytecodealliance/wasmtime/pull/14819
- https://github.com/bytecodealliance/wasmtime/pull/14820
- https://github.com/bytecodealliance/wasmtime/pull/14826
- https://github.com/bytecodealliance/wasmtime/releases/tag/v36.0.19
- https://github.com/bytecodealliance/wasmtime/releases/tag/v48.0.7
- https://github.com/bytecodealliance/wasmtime/releases/tag/v49.0.4
- https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-mghf-wjfp-p5xm
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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