CVE-2021-33880 is a medium-severity (CVSS 5.9) CWE-203 vulnerability in websockets. A fix is available for websockets — see the affected versions and patch details below.
Observable Timing Discrepancy in aaugustin websockets library
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-33880 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
websocketsReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
The aaugustin websockets library before 9.1 for Python has an Observable Timing Discrepancy on servers when HTTP Basic Authentication is enabled with basic_auth_protocol_factory(credentials=...). An attacker may be able to guess a password via a timing attack.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | websockets | all versions | 9.1pip install --upgrade 'websockets==9.1' |
Affected Products
communications cloud native core policyoraclecommunications cloud native core security edge protection proxyoraclecommunications cloud native core service communication proxyoraclecommunications cloud native core unified data repositoryoraclewebsocketswebsockets_projectDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for websockets, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update websockets to 9.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-33880 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
Is CVE-2021-33880 in your dependencies?
Find it across PyPI, including transitive dependencies.