How severe is GHSA-66p5-j55p-32r9?

No CVSS score has been assigned to GHSA-66p5-j55p-32r9 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by GHSA-66p5-j55p-32r9?

GHSA-66p5-j55p-32r9 affects the following packages: smallvec (crates.io). Ecosystems affected: crates.io.

How do I fix GHSA-66p5-j55p-32r9?

Update smallvec to 0.6.13 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-66p5-j55p-32r9 is resolved across your whole dependency graph.

How do I detect GHSA-66p5-j55p-32r9 in my crates.io dependencies?

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.

How do I mitigate GHSA-66p5-j55p-32r9 if there is no patch (or I can't update yet)?

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.

Is GHSA-66p5-j55p-32r9 actively exploited in the wild?

Yes. There are 1 known exploit references for GHSA-66p5-j55p-32r9, including 1 in-the-wild exploitation observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for GHSA-66p5-j55p-32r9?

GHSA-66p5-j55p-32r9 has an EPSS (Exploit Prediction Scoring System) score of 1.4%, placing it in the 73th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is GHSA-66p5-j55p-32r9?

GHSA-66p5-j55p-32r9 is classified as CWE-908 (CWE-908). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was GHSA-66p5-j55p-32r9 published, and has it been updated?

GHSA-66p5-j55p-32r9 was published on August 25, 2021 and was last updated on November 8, 2023. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🦀 crates.io

Not in CISA KEV

smallvec creates uninitialized value of any typeGHSA-66p5-j55p-32r9

Fix: servo/rust-smallvec#162

GHSA-66p5-j55p-32r9 is a CWE-908 vulnerability in smallvec. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for smallvec — see the affected versions and patch details below.

Also known asCVE-2018-25023 GHSA-55m5-whcv-c49cRUSTSEC-2018-0018

Published

Aug 25, 2021

Updated

Nov 8, 2023

Affected

1 pkg

Patched

1 / 1

Exploits

1 known

Exploitation data as of Nov 6, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for GHSA-66p5-j55p-32r9.

EPSS Exploitation Probability

via FIRST.org ↗

1.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs73th percentile — riskier than 73% of all scored CVEsHighest risk

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

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

Affected versions of this crate called mem::uninitialized() to create values of a user-supplied type T. This is unsound e.g. if T is a reference type (which must be non-null and thus may not remain uninitialized).

The flaw was corrected by avoiding the use of mem::uninitialized(), using MaybeUninit instead.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🦀crates.io	`smallvec`	all versions	0.6.13`cargo update -p smallvec --precise 0.6.13`

Affected Products

1 product · 1 configurations

Application

smallvecservo

< 0.6.13

range

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

An issue was discovered in the smallvec crate before 0.6.13 for Rust. It…

rustsec.orgNVDJan 2022

Detection & mitigation playbook

Open-source dependency

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.
Fix
Update smallvec to 0.6.13 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-66p5-j55p-32r9 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.

Frequently Asked Questions

Affected versions of this crate called `mem::uninitialized()` to create values of a user-supplied type `T`. This is unsound e.g. if `T` is a reference type (which must be non-null and thus may not remain uninitialized). The flaw was corrected by avoiding the use of `mem::uninitialized()`, using `MaybeUninit` instead.