How severe is CVE-2020-35865?

CVE-2020-35865 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2020-35865?

CVE-2020-35865 affects the following packages: os_str_bytes (crates.io). Ecosystems affected: crates.io.

How do I fix CVE-2020-35865?

Update os_str_bytes to 2.0.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-35865 is resolved across your whole dependency graph.

How do I detect CVE-2020-35865 in my crates.io dependencies?

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

How do I mitigate CVE-2020-35865 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 CVE-2020-35865 actively exploited in the wild?

No public exploit code has been indexed for CVE-2020-35865 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2020-35865?

CVE-2020-35865 has an EPSS (Exploit Prediction Scoring System) score of 1.4%, placing it in the 71th 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-2020-35865 published, and has it been updated?

CVE-2020-35865 was published on December 31, 2020 and was last updated on July 9, 2026. 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

HIGH severity

CVE-2020-35865 — os_str_bytes

HIGHFix: dylni/os_str_bytes#1

CVE-2020-35865 is a high-severity (CVSS 7.5) vulnerability in os_str_bytes. A fix is available for os_str_bytes — see the affected versions and patch details below.

os_str_bytes relies on undefined behavior of `char::from_u32_unchecked`

Also known asGHSA-q948-x8rf-888mRUSTSEC-2020-0012

Published

Dec 31, 2020

Updated

Jul 9, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

1.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs71th percentile — riskier than 71% of all scored CVEsHighest risk

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

How urgent is this, really

CVE-2020-35865 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,386 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

🦀os_str_bytes

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

The Windows implementation of this crate relied on the behavior of std::char::from_u32_unchecked when its safety clause is violated. Even though this worked with Rust versions up to 1.42 (at least), that behavior could change with any new Rust version, possibly leading a security issue.

The flaw was corrected in version 2.0.0.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🦀crates.io	`os_str_bytes`	all versions	2.0.0`cargo update -p os_str_bytes --precise 2.0.0`

Affected Products

1 product · 1 configurations

Application

os str bytesos_str_bytes_project

< 2.0.0

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for os_str_bytes, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update os_str_bytes to 2.0.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-35865 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

O3 Security · Impact-Aware SCA

Is CVE-2020-35865 in your dependencies?

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