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CRITICAL severity

CVE-2018-20991 — smallvec

CRITICAL

CVE-2018-20991 is a critical-severity (CVSS 9.8) CWE-415 vulnerability in smallvec. A fix is available for smallvec — see the affected versions and patch details below.

Double free in smallvec

Also known asGHSA-rxr4-x558-x7hwRUSTSEC-2018-0003
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Nov 2, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
1.8%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs79th percentile — riskier than 79% of all scored CVEsHighest risk
0.00%0.78%1.57%2.35%0.4%1.8%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected
🦀smallvec

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.

Description

If an iterator passed to SmallVec::insert_many 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.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🦀crates.iosmallvec≥ 0.3.2&&< 0.6.30.6.3cargo update -p smallvec --precise 0.6.3

Affected Products

1 product · 1 configurations
Application
smallvecservo
≥ 0.3.2 && < 0.6.3
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for smallvec, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update smallvec to 0.6.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2018-20991 is resolved across your whole dependency graph.

  3. Workarounds

    Constrain what reaches the vulnerable code: limit the size and shape of untrusted input, isolate the affected component in a sandboxed or least-privileged process, and enable the platform's memory-safety mitigations (ASLR, stack protector, hardened allocator) so an out-of-bounds access is more likely to fail closed than to be exploitable.

Frequently Asked Questions

If an iterator passed to SmallVec::insert_many 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.
O3 Security · Impact-Aware SCA

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CVE-2018-20991: smallvec — Fixed in 0.6.3