Improper Access Control in OnionshareGHSA-gjj5-998g-v36v
MEDIUMGHSA-gjj5-998g-v36v is a medium-severity (CVSS 4.3) Improper Authentication vulnerability in onionshare-cli. 1 public exploit reference exists, so weaponization risk is real. A fix is available for onionshare-cli — see the affected versions and patch details below.
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for GHSA-gjj5-998g-v36v.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
GHSA-gjj5-998g-v36v 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
onionshare-cliReal-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
Between September 26, 2021 and October 8, 2021, Radically Open Security conducted a penetration test of OnionShare 2.4, funded by the Open Technology Fund's Red Team lab. This is an issue from that penetration test.
- Vulnerability ID: OTF-003
- Vulnerability type: Improper Access Control
- Threat level: Moderate
Description:
Anyone with access to the chat environment can write messages disguised as another chat participant.
Technical description:
Prerequisites:
- Alice and Bob are legitimate users
- A third user has access to the chat environment
This screenshot shows Alice (glimpse-depress) and Bob (blinker-doorpost) joined a chatroom and are the only participants in the chatroom. Then the non-listed user squad-nursing writes a message in the chatroom without being visible in the list of users. The sending of the message itself is not required but was done here to show the initial access. The non-listed participant now renames himself to Bob and writes another message, seemingly coming from Bob.
This can be reproduced by slightly modifying the client-side JavaScript. The joined emit needs to be removed from the socket.on(connect) event handler. Therefore a client is not listed in the userlist and has no active session.
This can be done either via a crafted client or runtime modification of the chat.js script in the browser's internal debugger.
It is still possible to call the text method and send text to the chat via websocket.
It is also possible to call the update_username function and choose an existing username from the chat.
Afterwards the hidden user can send messages that are displayed as coming from the impersonated user. There is no way to distinguish between the fake and original message.
Impact:
An adversary with access to the chat environment can impersonate existing chat participants and write messages but not read the conversation. The similar exploit described in OTF-004 (page 19) has only slightly more requirements but also allows for reading.
Recommendation:
- Implement proper session handling
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | onionshare-cli | ≥ 2.3&&< 2.5 | 2.5pip install --upgrade 'onionshare-cli==2.5' |
Affected Products
onionshareonionshareResearch 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 onionshare-cli, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update onionshare-cli to 2.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-gjj5-998g-v36v is resolved across your whole dependency graph.
Workarounds
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.
Frequently Asked Questions
Is GHSA-gjj5-998g-v36v in your dependencies?
Find it across PyPI, including transitive dependencies.