How severe is CVE-2021-28032?

CVE-2021-28032 has a CVSS score of 9.8/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-28032?

CVE-2021-28032 affects the following packages: nano_arena (crates.io). Ecosystems affected: crates.io.

How do I fix CVE-2021-28032?

Update nano_arena to 0.5.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-28032 is resolved across your whole dependency graph.

How do I detect CVE-2021-28032 in my crates.io dependencies?

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

How do I mitigate CVE-2021-28032 if there is no patch (or I can't update yet)?

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.

Is CVE-2021-28032 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2021-28032, 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 CVE-2021-28032?

CVE-2021-28032 has an EPSS (Exploit Prediction Scoring System) score of 1.5%, placing it in the 74th 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.

When was CVE-2021-28032 published, and has it been updated?

CVE-2021-28032 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

CRITICAL severity

CVE-2021-28032 — nano_arena

CRITICALFix: bennetthardwick/nano-arena@6b83f9d

CVE-2021-28032 is a critical-severity (CVSS 9.8) vulnerability in nano_arena. 1 public exploit reference exists, so weaponization risk is real. A fix is available for nano_arena — see the affected versions and patch details below.

Use after free in nano_arena

Also known asRUSTSEC-2021-0031

Published

Aug 25, 2021

Updated

Nov 8, 2023

Affected

1 pkg

Patched

1 / 1

Exploits

1 known

Exploitation data as of Oct 8, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

1.5%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs74th percentile — riskier than 74% of all scored CVEsHighest risk

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

How urgent is this, really

CVE-2021-28032 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

🦀nano_arena

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 assumed that Borrow<Idx> was guaranteed to return the same value on .borrow(). The borrowed index value was used to retrieve a mutable reference to a value.

If the Borrow<Idx> implementation returned a different index, the split arena would allow retrieving the index as a mutable reference creating two mutable references to the same element. This violates Rust's aliasing rules and allows for memory safety issues such as writing out of bounds and use-after-frees.

The flaw was corrected in commit 6b83f9d by storing the .borrow() value in a temporary variable.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🦀crates.io	`nano_arena`	all versions	0.5.2`cargo update -p nano_arena --precise 0.5.2`

Affected Products

1 product · 1 configurations

Application

nano arenanano_arena_project

< 0.5.2

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 nano_arena crate before 0.5.2 for Rust. T…

rustsec.orgNVDMar 2021

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for nano_arena, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update nano_arena to 0.5.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-28032 is resolved across your whole dependency graph.
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

Affected versions of this crate assumed that Borrow<Idx> was guaranteed to return the same value on .borrow(). The borrowed index value was used to retrieve a mutable reference to a value. If the Borrow<Idx> implementation returned a different index, the split arena would allow retrieving the index as a mutable reference creating two mutable references to the same element. This violates Rust's aliasing rules and allows for memory safety issues such as writing out of bounds and use-after-frees. The flaw was corrected in commit `6b83f9d` by storing the .borrow() value in a temporary variable.

O3 Security · Impact-Aware SCA

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