python-engineio
CVE-2026-48802
HIGH
GHSA-cgwc-pv48-fhj5
Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Network-reachable Engine.IO endpoint, low-complexity PONG flooding, no auth required in default deployments, availability-only DoS with no confidentiality or integrity impact.
Primary rating from GitHub Advisory.
CVSS VectorGitHub Advisory
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Lifecycle Timeline
2DescriptionGitHub Advisory
Impact
An attacker can cause the creation of unnecessary background threads in the python-engineio server by exploiting the heartbeat mechanism, which launches a thread when a new connection is received, and when the client sends a PONG packet.
Note: this issue primarily affects synchronous servers. Asynchronous servers allocate background tasks instead of physical threads, which are lightweight and less likely to cause denial of service. However, the fix that was implemented was also applied to the asynchronous case.
Patches
Version 4.13.2 addresses this issue as follows:
- The initial background thread (or async task( for heartbeat management is only launched if a client passes authentication in the
connecthandler. - The server now ensures that there is only one background heatbeat thread (or async task) per client at a given point in time. Out of sequence PONG packets are now discarded when an active heartbeat thread is already running.
Articles & Coverage 1
AnalysisAI
Denial of service in the python-engineio server (versions <= 4.13.1) allows remote unauthenticated attackers to exhaust server resources by abusing the heartbeat mechanism, which spawns a new background thread on each connection and on every PONG packet received. Synchronous servers are most at risk because each heartbeat is a physical OS thread; asynchronous deployments allocate lightweight tasks and are far less affected. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation targets the Engine.IO heartbeat mechanism: the attacker must be able to reach the server's Engine.IO endpoint over the network and send PONG packets, particularly out-of-sequence ones, to trigger repeated background worker creation. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The provided CVSS 3.1 vector (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H, score 7.5 HIGH) describes a network-reachable, low-complexity, unauthenticated attack with availability-only impact and no confidentiality or integrity effect - consistent with a pure DoS. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker opens an Engine.IO connection to a synchronous python-engineio server and then repeatedly sends out-of-sequence PONG packets, each of which causes the server to spawn an additional background heartbeat thread. By scripting many connections and PONG floods, the attacker drives unbounded thread creation until the server exhausts memory or scheduling capacity and stops serving legitimate users. … |
| Remediation | Vendor-released patch: 4.13.2 - upgrade python-engineio to 4.13.2 or later (for example via 'pip install --upgrade python-engineio>=4.13.2'), per the advisory at https://github.com/miguelgrinberg/python-engineio/security/advisories/GHSA-cgwc-pv48-fhj5. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours: Audit all systems running python-engineio ≤4.13.1; identify deployment architecture (sync vs. …
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External POC / Exploit Code
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