CVE-2026-48804 is a high-severity (CVSS 7.5) CWE-770 vulnerability in python-socketio. A fix is available for python-socketio — see the affected versions and patch details below.
python-socketio: Binary attachment accumulation can cause denial of service
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-48804.
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
python-socketioReal-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
python-socketio is a Python implementation of the Socket.IO realtime client and server. The python-socketio server stores binary EVENT and ACK messages in memory while it waits to receive their binary attachments. Once all the attachments are received, these messages are then processed. Prior to version 5.16.4, an attacker can submit a binary message and intentionally omit sending one or more of its attachments to cause the message along with the partial list of received attachments to stay in memory for a long time. Version 5.16.4 takes the following measures to address this issue: Binary packets are only accepted from authenticated clients and, when a client disconnects, the server checks if there is a partial binary message being held for the client and deletes it.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | python-socketio | all versions | 5.16.2pip install --upgrade 'python-socketio==5.16.2' |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for python-socketio, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update python-socketio to 5.16.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-48804 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
A denial of service flaw exists in python-socketio's binary packet assembly mechanism. When handling incoming binary EVENT and ACK payloads, the server retains incomplete messages and partial attachments in memory while awaiting remaining attachments. An unauthenticated remote attacker can submit binary headers while…
Require authentication for all client connections before accepting socket requests, or enforce connection timeouts at the reverse proxy layer to disconnect incomplete binary payload streams.Source: Red Hat security advisory for CVE-2026-48804 (CC BY 4.0)
Frequently Asked Questions
Is CVE-2026-48804 in your dependencies?
Find it across PyPI, including transitive dependencies.