CVE-2021-4171 is a critical-severity (CVSS 9.8) CWE-840 vulnerability in calibreweb. 1 public exploit reference exists, so weaponization risk is real. A fix is available for calibreweb — see the affected versions and patch details below.
calibre-web is vulnerable to Business Logic Errors
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-4171 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
calibrewebReal-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
calibre-web is vulnerable to Business Logic Errors
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | calibreweb | all versions | 0.6.15pip install --upgrade 'calibreweb==0.6.15' |
Affected Products
calibre-webjaneczkuResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for calibreweb, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update calibreweb to 0.6.15 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-4171 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-2021-4171 in your dependencies?
Find it across PyPI, including transitive dependencies.