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Double free in StackVec::retain when a predicate or element Drop panics

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (stack_collections 0.3.3), 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
not scored
EPSS
No dated EPSS signal available.
Source description

As published by the source; long descriptions are shortened.

Summary `StackVec::retain` committed its new length to `self.len` only after its internal loop completed. If the retain predicate or a removed element's `Drop` implementation panicked before the loop finished, unwinding proceeded with `self.len` still equal to the original, pre-retain length, leaving either a duplicated or already-destroyed element inside `0..len`. `StackVec`'s own `Drop` then revisited that slot, causing a double-drop (and for heap-owning types, a double-free).

Impact Affects `StackVec ::retain` for `T: Drop` types where the predicate or the removed element's destructor can panic, on builds with unwinding enabled (`panic = "unwind"`). `no_std`/`panic = "abort"` builds cannot trigger this, since unwinding never occurs.

Patch Fixed in 0.3.3 using an unwind-safe backshift guard, matching the approach `alloc::vec::Vec::retain` uses.

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

    Published from osv record RUSTSEC-2026-0301

Agent brief

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

# Patch Next advisory brief: rustsec-2026-0301

Advisory: Double free in `StackVec::retain` when a predicate or element `Drop` panics
IDs: rustsec-2026-0301
Record: https://patchnext.com/advisories/rustsec-2026-0301 (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: stack_collections 0.3.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io stack_collections: affected >= 0.3.0, < 0.3.3; fixed in 0.3.3

## Suggested inspection (read-only)
- crates.io stack_collections: 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 stack_collections.
- 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-2026-0301 (OSV record RUSTSEC-2026-0301 lists affected ranges: crates.io stack_collections >=0.3.0 <0.3.3 (fixed))

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