Out-of-Bounds Read in Wasmtime (CVE-2026-34971)
Summary
Vulnerability in Wasmtime (CVE-2026-34971). Successful exploitation can lead to full system takeover. Mitigation: upgrade to 36.0.7 or later.
Original description
The description as published by the source.
Wasmtime is a runtime for WebAssembly. From 32.0.0 to before 36.0.7, 42.0.2, and 43.0.1, Wasmtime's Cranelift compilation backend contains a bug on aarch64 when performing a certain shape of heap accesses which means that the wrong address is accessed. When combined with explicit bounds checks a guest WebAssembly module this can create a situation where there are two diverging computations for the same address: one for the address to bounds-check and one for the address to load. This difference in address being operated on means that a guest module can pass a bounds check but then load a different address. Combined together this enables an arbitrary read/write primitive for guest WebAssembly when accesssing host memory. This is a sandbox escape as guests are able to read/write arbitrary host memory. This vulnerability has a few ingredients, all of which must be met, for this situation to occur and bypass the sandbox restrictions. This miscompiled shape of load only occurs on 64-bit WebAssembly linear memories, or when Config::wasm_memory64 is enabled. 32-bit WebAssembly is not affected. Spectre mitigations or signals-based-traps must be disabled. When spectre mitigations are enabled then the offending shape of load is not generated. When signals-based-traps are disabled then spectre mitigations are also automatically disabled. The specific bug in Cranelift is a miscompile of a load of the shape load(iadd(base, ishl(index, amt))) where amt is a constant. The amt value is maske…
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-34971 has been found in Wasmtime.
Successful exploitation can lead to full system takeover. CVSS score: 7.8/10.
What to do: upgrade Wasmtime to 36.0.7 or later.
If unsure, ask your IT team or search "Wasmtime CVE-2026-34971" on the vendor's site.
CVE-2026-34971 (Wasmtime) — CWE-125 / CVSS v3 7.8
Attack vector: local / no user interaction
Patched: 36.0.7 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
Out-of-bounds read (CWE-125) exists in Wasmtime.
Check the vendor advisory for the affected versions of Wasmtime.
Severity: High (CVSS 7.8/10). Successful exploitation can lead to full system takeover.
Update to 36.0.7.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'Wasmtime' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'Wasmtime' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
Wasmtimeを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade Wasmtime to 36.0.7ステージング環境で 36.0.7 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2026-34971 rust-wasmtime
- Ubuntu UBUNTU-CVE-2026-34971 rust-wasmtime
References
- advisory github.com
- advisory access.redhat.com
- advisory rustsec.org
- advisory github.com
- advisory nvd.nist.gov
- package crates.io
- report bugzilla.redhat.com
- web security.access.redhat.com
- web github.com