# CVE-2026-34988: Wasmtime leaks data between pooling allocator instances > Attackers can read memory from previous WebAssembly instances due to improper permission resets in Wasmtime's pooling allocator under specific non-default configurations. - **Severity:** Low 2.3 (`CVSS:4.0/AV:N/AC:H/AT:P/PR:L/UI:N/VC:L/VI:N/VA:N/SC:L/SI:N/SA:N`) - **Exploited in the wild:** Not known - **Login needed:** Any signed-in user - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 9 Apr 2026 - **Updated:** 9 Apr 2026 - **Also known as:** DEBIAN-CVE-2026-34988, GHSA-6wgr-89rj-399p, JLSEC-2026-1362, RUSTSEC-2026-0088, UBUNTU-CVE-2026-34988 ## What is CVE-2026-34988? CVE-2026-34988 is a low-severity vulnerability in bytecodealliance wasmtime, published on 9 Apr 2026. Any signed-in user can exploit it over the network, with no action from the victim. ### Official description Wasmtime is a runtime for WebAssembly. From 28.0.0 to before 36.0.7, 42.0.2, and 43.0.1, Wasmtime's implementation of its pooling allocator contains a bug where in certain configurations the contents of linear memory can be leaked from one instance to the next. The implementation of resetting the virtual memory permissions for linear memory used the wrong predicate to determine if resetting was necessary, where the compilation process used a different predicate. This divergence meant that the pooling allocator incorrectly deduced at runtime that resetting virtual memory permissions was not necessary while compile-time determine that virtual memory could be relied upon. The pooling allocator must be in use, Config::memory_guard_size configuration option must be 0, Config::memory_reservation configuration must be less than 4GiB, and pooling allocator must be configured with max_memory_size the same as the memory_reservation value in order to exploit this vulnerability. If all of these conditions are applicable then when a linear memory is reused the VM permissions of the previous iteration are not reset. This means that the compiled code, which is assuming out-of-bounds loads will segfault, will not actually segfault and can read the previous contents of linear memory if it was previously mapped. This represents a data leakage vulnerability between guest WebAssembly instances which breaks WebAssembly's semantics and additionally breaks the sandbox that Wasmtime provides. Wasmtime is not vulnerable to this issue with its default settings, nor with the default settings of the pooling allocator, but embeddings are still allowed to configure these values to cause this vulnerability. This vulnerability is fixed in 36.0.7, 42.0.2, and 43.0.1. Weakness: CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer) ## Which versions are affected by CVE-2026-34988? 7 open source packages ship an affected version, including wasmtime. It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `wasmtime` | crates.io | From 0.0.0-0 | 36.0.7, 42.0.2, 43.0.1 | | `wasmtime` | crates.io | From 28.0.0 | 36.0.7 | | `wasmtime` | crates.io | From 28.0.0 | 36.0.7 | | `wasmtime` | crates.io | From 37.0.0 | 42.0.2 | | `wasmtime` | crates.io | From 37.0.0 | 42.0.2 | | `wasmtime` | crates.io | From 43.0.0 | 43.0.1 | | `wasmtime` | crates.io | From 43.0.0 | 43.0.1 | Products: Bytecodealliance Wasmtime. ## How do I fix CVE-2026-34988? Upgrade wasmtime to a fixed version for your release line: 36.0.7, 42.0.2 or 43.0.1. ## Is CVE-2026-34988 being exploited? There is no known exploitation of CVE-2026-34988 in the wild and no public exploit code. ## Other vulnerabilities in bytecodealliance wasmtime - [CVE-2026-34971](https://insights.sbomify.com/CVE-2026-34971/): Wasmtime miscompiled guest heap access enables sandbox escape on aarch64 Cranelift (critical 9.0) - [CVE-2026-34987](https://insights.sbomify.com/CVE-2026-34987/): Wasmtime with Winch compiler backend on aarch64 may allow a sandbox-escaping memory access (critical 9.0) - [CVE-2022-39393](https://insights.sbomify.com/CVE-2022-39393/): Wasmtime vulnerable to data leakage between instances in the pooling allocator (high 8.6) - [CVE-2022-24791](https://insights.sbomify.com/CVE-2022-24791/): Use after free in Wasmtime (high 8.1) - [CVE-2026-47261](https://insights.sbomify.com/CVE-2026-47261/): Wasmtime: WASI path_open(TRUNCATE) bypasses `FilePerms::WRITE` host restriction (high 7.5) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-34988 and fix it if it is affected. What it is: CVE-2026-34988 is a low-severity vulnerability in bytecodealliance wasmtime, published on 9 Apr 2026. Any signed-in user can exploit it over the network, with no action from the victim. Exploitation: There is no known exploitation of CVE-2026-34988 in the wild and no public exploit code. Affected packages and fixed versions: - wasmtime (crates.io): affected from 0.0.0-0; fixed in 36.0.7, 42.0.2, 43.0.1 - wasmtime (crates.io): affected from 28.0.0; fixed in 36.0.7 - wasmtime (crates.io): affected from 28.0.0; fixed in 36.0.7 - wasmtime (crates.io): affected from 37.0.0; fixed in 42.0.2 - wasmtime (crates.io): affected from 37.0.0; fixed in 42.0.2 - wasmtime (crates.io): affected from 43.0.0; fixed in 43.0.1 - wasmtime (crates.io): affected from 43.0.0; fixed in 43.0.1 Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-34988/ (Markdown: https://insights.sbomify.com/CVE-2026-34988/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-34988 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-34988 - OSV: https://osv.dev/vulnerability/CVE-2026-34988 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-34988/ Summaries are generated and may contain mistakes; the official description above is the record.