unbounded-spsc: Sender::send pointer-as-value transmute causes OOB read and fake-Arc drop under TX/RX race

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

5.8 · CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H

EPSS

• CVE-2026-46690: 0.13% estimated exploitation activity in the next 30 days; percentile 2.65 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary Sender::send in src/lib.rs contains an unsafe block in the DISCONNECTED arm that transmutes a raw pointer (mut Producer<T) into the bytes of a value-level Consumer<T. The author's intent, visible in the surrounding comment at lines 386-390, was a value transmute. The shipped code is one level of indirection off. The resulting Consumer<T has its internal Arc::ptr set to the address of the producer field on the Sender, not the real ArcInner<Buffer<T. Every subsequent consumer.trypop() walks Buffer<T fields at offsets that lie inside the Sender<T struct (over sendnew, inner) and adjacent memory, an out-of-bounds read. When the fake Consumer<T is dropped at the end of the unsafe block, its Drop calls Arc::dropinplace on a non-ArcInner address: it decrements bytes that the type system treats as strongcount: AtomicUsize but that are actually the real Arc::ptr value of the Sender, and at zero count it calls dealloc(Layout::forvalue(...)) on an address the allocator never returned.…

Published by the source

29 May 2026, 19:05 UTC

Last modified by the source

12 Jun 2026, 19:31 UTC

Source last checked

26 Oct 2026, 15:42 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-6m57-8r3p-pqx6

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-46690

Advisory: unbounded-spsc: Sender::send pointer-as-value transmute causes OOB read and fake-Arc drop under TX/RX race
IDs: CVE-2026-46690, GHSA-6m57-8r3p-pqx6
Record: https://patchnext.com/advisories/cve-2026-46690 (revision 1, 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: Medium (CVSS 5.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor response not established. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io unbounded-spsc: affected <= 0.2.0

## Suggested inspection (read-only)
- crates.io unbounded-spsc: 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 unbounded-spsc.
- 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://github.com/advisories/GHSA-6m57-8r3p-pqx6 (GitHub-reviewed advisory GHSA-6m57-8r3p-pqx6 lists affected ranges: crates.io unbounded-spsc >=0 <=0.2.0)

Commands are suggestions: review each one before running it.