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Low, CVSS 1.0amended

Wasmtime has use-after-free bug after cloning wasmtime::Linker

CVE-2026-34983GHSA-hfr4-7c6c-48w2

What to do

Partial vendor fix. Follow the primary source's mitigation guidance and check back for a fix.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • PyPI wasmtime

    Affected
    <= 43.0.0
    Fixed in
    no fixed version recorded

  • crates.io wasmtime

    Affected
    >= 43.0.0, <= 43.0.0
    Fixed in
    43.0.1

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
1.0 · CVSS:4.0/AV:P/AC:H/AT:P/PR:H/UI:A/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N · score source
EPSS
  • CVE-2026-34983: 0.12% estimated exploitation activity in the next 30 days; percentile 1.66 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Impact In version 43.0.0 of the wasmtime crate, cloning a wasmtime::Linker is unsound and can result in use-after-free bugs. This bug is not controllable by guest Wasm programs. It can only be triggered by a specific sequence of embedder API calls made by the host. The typical symptom of this use-after-free bug is a segfault. It does not enable heap corruption or data leakage. If you are using the wasmtime CLI, rather than the embedding API, you are not affected. If you are using the embedding API but are not calling wasmtime::Linker's Clone implementation, you are not affected. Specifically, the following steps must occur to trigger the bug: Clone a wasmtime::Linker Drop the original linker instance Use the new, cloned linker instance, resulting in a use-after-free Patches This bug has been patched in Wasmtime version 43.0.1 Workarounds Wasmtime embedders are highly encouraged to upgrade their wasmtime crate dependency. If upgrading is not an option, or as a temporary workaround…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-hfr4-7c6c-48w2

  2. Revision 2 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  3. Revision 1 · created ·

    Published from osv record PYSEC-2026-151

Agent brief

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# Patch Next advisory brief: CVE-2026-34983

Advisory: Wasmtime has use-after-free bug after cloning `wasmtime::Linker`
IDs: CVE-2026-34983, GHSA-hfr4-7c6c-48w2
Record: https://patchnext.com/advisories/cve-2026-34983 (revision 3, source checked 26 Oct 2026, 15:42 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 1.0)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Partial vendor fix; fixed versions by package: wasmtime 43.0.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI wasmtime: affected <= 43.0.0
- crates.io wasmtime: affected >= 43.0.0, <= 43.0.0; fixed in 43.0.1

## Suggested inspection (read-only)
- `python -m pip show wasmtime`: prints the installed version. Run with the environment that serves production active.
- crates.io wasmtime: check the installed version with your package manager.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on wasmtime.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/PYSEC-2026-151 (OSV record PYSEC-2026-151 lists affected ranges: PyPI wasmtime >=0 <=43.0.0)
- Verified: https://github.com/advisories/GHSA-hfr4-7c6c-48w2 (GitHub-reviewed advisory GHSA-hfr4-7c6c-48w2 lists affected ranges: crates.io wasmtime >=43.0.0 <=43.0.0)

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