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Low, CVSS 1.0amended

Wasmtime: Memory leak in C API with externref and anyref types

CVE-2025-61670GHSA-vvp9-h8p2-xwfc

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (wasmtime-c-api-impl 37.0.2; wasmtime-bin 37.0.2), redeploy, then verify what is actually installed.

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

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:A/AC:L/AT:P/PR:L/UI:P/VC:N/VI:N/VA:L/SC:N/SI:N/SA:L · score source
EPSS
  • CVE-2025-61670: 0.19% estimated exploitation activity in the next 30 days; percentile 9.33 (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 Wasmtime 37.0.0 and 37.0.1 have memory leaks in the C/C++ API when using bindings for the anyref or externref WebAssembly values. This is caused by a regression introduced during the development of 37.0.0 and all prior versions of Wasmtime are unaffected. If anyref or externref is not used in the C/C++ API then embeddings are also unaffected by the leaky behavior. The wasmtime Rust crate is unaffected by this leak. Development of Wasmtime 37.0.0 included a refactoring in Rust of changing the old ManuallyRooted<T type to a new OwnedRooted<T type. This change was integrated into Wasmtime's C API but left the C API in a state which had memory leaks. Additionally the new ownership semantics around this type were not reflected into the C++ API, making it leak-prone. A short version of the change is that previously ManuallyRooted<T, as the name implies, required manual calls to an "unroot" operation. If this was forgotten then the memory was still cleaned up when the wasmtimestoret…

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

    Amended from ghsa record GHSA-vvp9-h8p2-xwfc

  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 GHSA-vvp9-h8p2-xwfc

Agent brief

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# Patch Next advisory brief: CVE-2025-61670

Advisory: Wasmtime: Memory leak in C API with `externref` and `anyref` types
IDs: CVE-2025-61670, GHSA-vvp9-h8p2-xwfc
Record: https://patchnext.com/advisories/cve-2025-61670 (revision 3, source checked 26 Oct 2026, 13:46 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: Vendor fix available; fixed versions by package: wasmtime-c-api-impl 37.0.2; wasmtime-bin 37.0.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io wasmtime-c-api-impl: affected >= 37.0.0, < 37.0.2; fixed in 37.0.2
- PyPI wasmtime-bin: affected < 37.0.2; fixed in 37.0.2

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

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on wasmtime-c-api-impl, wasmtime-bin.
- 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/GHSA-vvp9-h8p2-xwfc (OSV record GHSA-vvp9-h8p2-xwfc lists affected ranges: crates.io wasmtime-c-api-impl >=37.0.0 =0 <37.0.2 (fixed))
- Verified: https://github.com/advisories/GHSA-vvp9-h8p2-xwfc (GitHub-reviewed advisory GHSA-vvp9-h8p2-xwfc lists affected ranges: crates.io wasmtime-c-api-impl >=37.0.0 =0 <37.0.2)

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