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AsyncFd::new and related constructors violate I/O safety

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (tokio 1.53.3, 1.51.6), 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

  • crates.io tokio

    Affected
    >= 0.3.2, < 1.51.6>= 1.52.0, < 1.53.3
    Fixed in
    1.51.6, 1.53.3

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
not scored
EPSS
No dated EPSS signal available.
Source description

As published by the source; long descriptions are shortened.

`tokio::io::unix::AsyncFd` provides safe constructors (`new`, `with_interest`, `try_new`, and `try_with_interest`) that accept any `T: AsRawFd` rather than requiring proof of ownership or validity of the file descriptor. Because `RawFd` implements `AsRawFd`, safe code can construct an `AsyncFd` from an arbitrary or closed file descriptor, or close/replace the underlying file descriptor while the `AsyncFd` is still alive. This violates I/O safety in two ways: 1. `AsyncFd ` implements `AsFd` for all `T: AsRawFd` by calling `BorrowedFd::borrow_raw(self.as_raw_fd())`, allowing safe code to obtain an arbitrary `BorrowedFd ` without owning the file descriptor. 2. Tokio's I/O driver stores a pointer to an internal allocation in the `epoll`/`kqueue` user data for registered file descriptors. If the underlying file descriptor is duplicated and then closed while an `AsyncFd` is alive, and the OS reuses that file descriptor number for a another IO resource on the same runtime, dropping the…

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

    Published from osv record RUSTSEC-2026-0386

Agent brief

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# Patch Next advisory brief: rustsec-2026-0386

Advisory: `AsyncFd::new` and related constructors violate I/O safety
IDs: rustsec-2026-0386
Record: https://patchnext.com/advisories/rustsec-2026-0386 (revision 1, source checked 23 Oct 2026, 22:04 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Unrated
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: tokio 1.53.3, 1.51.6. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io tokio: affected >= 0.3.2, < 1.51.6; >= 1.52.0, < 1.53.3; fixed in 1.51.6, 1.53.3

## Suggested inspection (read-only)
- crates.io tokio: check the installed version with your package manager.

## 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 tokio.
- 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/RUSTSEC-2026-0386 (OSV record RUSTSEC-2026-0386 lists affected ranges: crates.io tokio >=0.3.2 =1.52.0 <1.53.3 (fixed))

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