CVE-2018-20991 — smallvec
CRITICALCVE-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
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2018-20991 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,636 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
smallvecReal-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
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | smallvec | ≥ 0.3.2&&< 0.6.3 | 0.6.3cargo update -p smallvec --precise 0.6.3 |
Detection & mitigation playbook
Open-source dependencyDetect
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.
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.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2018-20991 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2018-20991. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2018-20991 in your dependencies?
O3 Security finds CVE-2018-20991 across crates.io dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.