Double free in smallvec

Exploitation

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

CVSS

9.8 · CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS

• CVE-2018-20991: 1.85% estimated exploitation activity in the next 30 days; percentile 79.11 (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.

If an iterator passed to SmallVec::insertmany panicked in Iterator::next, destructors were run during unwinding while the vector was in an inconsistent state, possibly causing a double free (a destructor running on two copies of the same value). This is fixed in smallvec 0.6.3 by ensuring that the vector's length is not updated to include moved items until they have been removed from their original positions. Items may now be leaked if Iterator::next panics, but they will not be dropped more than once.

Published by the source

25 Aug 2021, 20:42 UTC

Last modified by the source

13 Jun 2023, 20:58 UTC

Source last checked

26 Oct 2026, 15:34 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-rxr4-x558-x7hw

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# Patch Next advisory brief: CVE-2018-20991

Advisory: Double free in smallvec
IDs: CVE-2018-20991, GHSA-rxr4-x558-x7hw
Record: https://patchnext.com/advisories/cve-2018-20991 (revision 1, source checked 26 Oct 2026, 15:34 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: smallvec 0.6.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io smallvec: affected >= 0.3.2, < 0.6.3; fixed in 0.6.3

## Suggested inspection (read-only)
- crates.io smallvec: 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 smallvec.
- 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-rxr4-x558-x7hw (GitHub-reviewed advisory GHSA-rxr4-x558-x7hw lists affected ranges: crates.io smallvec >=0.3.2 <0.6.3)

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