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Not in CISA KEV
HIGH severity

CVE-2020-36208 — conquer-once

HIGH

CVE-2020-36208 is a high-severity (CVSS 7.8) CWE-662 vulnerability in conquer-once. 1 public exploit reference exists, so weaponization risk is real. A fix is available for conquer-once — see the affected versions and patch details below.

Data races in conquer-once

Also known asGHSA-3jc5-5hc5-33gjRUSTSEC-2020-0101
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
1 known
Exploitation data as of Oct 9, 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 CVEs35th percentile — riskier than 35% of all scored CVEsHighest risk
0.00%0.31%0.62%0.93%0.1%0.4%Apr 26Aug 26Oct 26

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

How urgent is this, really

CVE-2020-36208 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
🦀conquer-once

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 conquer-once implements Sync for its OnceCell type without restricting it to Sendable types.

This allows non-Send but Sync types such as MutexGuard to be sent across threads leading to undefined behavior and memory corruption in concurrent programs.

The issue was fixed by adding a Send constraint to OnceCell.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🦀crates.ioconquer-onceall versions0.3.2cargo update -p conquer-once --precise 0.3.2

Affected Products

1 product · 1 configurations
Application
conquer-onceconquer-once_project
< 0.3.2
range
Exploits & PoCs
1

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 conquer-once crate before 0.3.2 for Rust.…

rustsec.orgNVDJul 2021

Detection & mitigation playbook

Open-source dependency

  1. Detect

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

  2. Fix

    Update conquer-once to 0.3.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-36208 is resolved across your whole dependency graph.

  3. 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 conquer-once implements Sync for its OnceCell type without restricting it to Sendable types. This allows non-Send but Sync types such as MutexGuard to be sent across threads leading to undefined behavior and memory corruption in concurrent programs. The issue was fixed by adding a Send constraint to OnceCell.
O3 Security · Impact-Aware SCA

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CVE-2020-36208: conquer-once — Fixed in 0.3.2