CVE-2021-40347 — postorius
MEDIUMCVE-2021-40347 is a medium-severity (CVSS 5.4) vulnerability in postorius. 2 public exploit or proof-of-concept references are indexed, so weaponization risk is real. A fix is available for postorius — see the affected versions and patch details below.
GNU Mailman Postorius Access Control Issues
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
postoriusReal-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
An issue was discovered in views/list.py in GNU Mailman Postorius before 1.3.5. An attacker (logged into any account) can send a crafted POST request to unsubscribe any user from a mailing list, also revealing whether that address was subscribed in the first place.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | postorius | all versions | 1.3.5pip install --upgrade 'postorius==1.3.5' |
Affected Products
postoriuspostorius_projectResearch 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 postorius, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update postorius to 1.3.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-40347 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-2021-40347 in your dependencies?
Find it across PyPI, including transitive dependencies.