# OSV-2026-603: UNKNOWN READ in ::call_unchecked_raw::< > An unknown read error in the Wasmtime runtime can cause a crash when calling functions, potentially leading to denial of service. - **Severity:** Not scored - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Not stated - **Victim action needed:** Not needed - **Fix available:** No - **Published:** 21 Apr 2026 ## What is OSV-2026-603? OSV-2026-603 is a memory corruption vulnerability in wasmtime, published on 21 Apr 2026. ### Official description OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=504268343 ``` Crash type: UNKNOWN READ Crash state: ::call_unchecked_raw::< ::call_impl_do_call::< wasmtime_internal_fiber::stackswitch::x86_64::wasmtime_fiber_start ``` ## Which versions are affected by OSV-2026-603? 1 open source package ship an affected version, including wasmtime. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `wasmtime` | OSS-Fuzz | All versions | None | ## How do I fix OSV-2026-603? No fix has been published for OSV-2026-603 yet. Limit exposure of the affected software until one is available. ## Is OSV-2026-603 being exploited? There is no known exploitation of OSV-2026-603 in the wild and no public exploit code. ## Fix prompt for AI coding agents ```text Check this codebase for OSV-2026-603 and fix it if it is affected. What it is: OSV-2026-603 is a memory corruption vulnerability in wasmtime, published on 21 Apr 2026. Exploitation: There is no known exploitation of OSV-2026-603 in the wild and no public exploit code. Affected packages and fixed versions: - wasmtime (OSS-Fuzz): affected all versions; no fix listed 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/OSV-2026-603/ (Markdown: https://insights.sbomify.com/OSV-2026-603/index.md) ``` ## Sources - OSV: https://osv.dev/vulnerability/OSV-2026-603 --- From sbomify Insights: https://insights.sbomify.com/OSV-2026-603/ Summaries are generated and may contain mistakes; the official description above is the record.