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Not in CISA KEV
MEDIUM severity

GNU Mailman Postorius Access Control IssuesGHSA-v83x-78q3-gr2j

MEDIUM

GHSA-v83x-78q3-gr2j 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.

Also known asCVE-2021-40347PYSEC-2021-319
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
2 known
Exploitation data as of Nov 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
1.2%probability of exploitation in next 30 days
Lower Risk+0.02%
Lower risk than most CVEs69th percentile — riskier than 69% of all scored CVEsHighest risk
0.00%0.57%1.14%1.71%0.2%1.2%May 26Sep 26Nov 26

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

1 pkg affected
🐍postorius

Real-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

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐍PyPIpostoriusall versions1.3.5pip install --upgrade 'postorius==1.3.5'

Affected Products

1 product · 1 configurations
Application
postoriuspostorius_project
< 1.3.5
range
Exploits & PoCs
2

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 views/list.py in GNU Mailman Postorius before…

gitlab.comNVDSep 2021

Report on phabricator.wikimedia.org

phabricator.wikimedia.orgNVDSep 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 postorius, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update postorius to 1.3.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-v83x-78q3-gr2j is resolved across your whole dependency graph.

  3. 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

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.
O3 Security · Impact-Aware SCA

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GNU Mailman Postorius Access Control Issues