Machine-written summary
Summary written by Claude Haiku from the source advisory. Not reviewed by a person.
python-engineio versions before 4.13.2 can be made to create unnecessary background threads on a server through its heartbeat mechanism, which starts a thread when a connection is received and when a client sends a PONG packet. The issue mainly affects synchronous servers, though the fix also covers asynchronous ones. Upgrade to python-engineio 4.13.2, which starts the heartbeat thread only after a client passes authentication in the connect handler and allows only one heartbeat thread per client.
Not analysed yet
We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.
Severity and exploitation
| Score | Rating | CVSS | Vector | Source |
|---|---|---|---|---|
| 7.5 | High | 3.1 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H | CNA (GitHub_M) |
- CISA KEV Not listed.
- EPSS 0.0057, the 47th percentile, on 15 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.
Timeline
- 31 Oct 2026, 15:02 UTC First seen by agentprime
- 31 Oct 2026, 15:02 UTC Confirmed by OSV