How severe is CVE-2020-35903?

CVE-2020-35903 has a CVSS score of 5.5/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2020-35903?

CVE-2020-35903 affects the following packages: dync (crates.io). Ecosystems affected: crates.io.

How do I fix CVE-2020-35903?

Update dync to 0.5.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-35903 is resolved across your whole dependency graph.

How do I detect CVE-2020-35903 in my crates.io dependencies?

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

How do I mitigate CVE-2020-35903 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-2020-35903 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2020-35903, 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-2020-35903?

CVE-2020-35903 has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 30th 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-2020-35903 published, and has it been updated?

CVE-2020-35903 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

MEDIUM severity

CVE-2020-35903 — dync

MEDIUM

CVE-2020-35903 is a medium-severity (CVSS 5.5) vulnerability in dync. 1 public exploit reference exists, so weaponization risk is real. A fix is available for dync — see the affected versions and patch details below.

Out of bounds read in dync

Also known asRUSTSEC-2020-0050

Published

Aug 25, 2021

Updated

Nov 8, 2023

Affected

1 pkg

Patched

1 / 1

Exploits

1 known

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

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs30th percentile — riskier than 30% of all scored CVEsHighest risk

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

How urgent is this, really

CVE-2020-35903 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

🦀dync

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

VecCopy::data is created as a Vec of u8 but can be used to store and retrieve elements of different types leading to misaligned access.

The issue was resolved in v0.5.0 by replacing data being stored by Vec<u8> with a custom managed pointer. Elements are now stored and retrieved using types with proper alignment corresponding to original types.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🦀crates.io	`dync`	all versions	0.5.0`cargo update -p dync --precise 0.5.0`

Affected Products

1 product · 1 configurations

Application

dyncdync_project

< 0.5.0

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 dync crate before 0.5.0 for Rust. VecCopy…

rustsec.orgNVDJan 2021

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for dync, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update dync to 0.5.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-35903 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

VecCopy::data is created as a Vec of u8 but can be used to store and retrieve elements of different types leading to misaligned access. The issue was resolved in v0.5.0 by replacing data being stored by Vec<u8> with a custom managed pointer. Elements are now stored and retrieved using types with proper alignment corresponding to original types.

O3 Security · Impact-Aware SCA

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