python-engineio
CVE-2026-48809
HIGH
GHSA-m9gh-vj53-gvh9
Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Network-reachable oversized messages with no privileges or interaction cause memory-exhaustion DoS (A:H), with no confidentiality or integrity impact; AC:L as flooding is straightforward.
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
There are two specific configurations of the python-engineio server in which the size of incoming messages is not checked before the messages are loaded into memory. An attacker can take advantage of these to cause unnecessary memory allocations in the python-engineio server. The two cases are:
- POST requests, when using ASGI with the long polling transport
- WebSocket messages, when using Aiohttp with the WebSocket transport
Patches
Version 4.13.2 addresses this issue as follows:
- ASGI severs now only load the body of incoming requests into memory after the client is confirmed to be known and authenticated, and the payload size is below the maximum allowed size. Requests that do not comply with these requirements are discarded.
- Aiohttp servers configure the maximum payload size in the underlying WebSocket layer from Aiohttp, so that large messages are discarded by Aiohttp before they are delivered to python-engineio.
Articles & Coverage 1
AnalysisAI
Uncontrolled memory allocation in python-engineio (versions <= 4.13.1) lets remote attackers exhaust server memory by sending oversized messages that are loaded before any size check, causing denial of service (availability-only impact). The flaw triggers in two specific transport configurations - ASGI with long-polling POST requests, and Aiohttp with the WebSocket transport - and is fixed in 4.13.2. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires the python-engineio server to be running one of two specific configurations: (1) ASGI deployment using the long-polling transport, exploited via oversized POST requests, or (2) Aiohttp deployment using the WebSocket transport, exploited via oversized WebSocket messages. … 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, base 7.5) reflects a network-reachable, low-complexity, unauthenticated availability-only impact - consistent with a resource-exhaustion DoS rather than data compromise (C:N/I:N). … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker identifies a service built on python-engineio running an affected transport (ASGI long-polling or Aiohttp WebSocket) and repeatedly sends very large POST bodies or WebSocket messages. Each oversized message is buffered into memory before the size limit is applied, and a sustained flood drives memory consumption up until the process is exhausted or OOM-killed, denying service to legitimate users. … |
| Remediation | Upgrade to python-engineio 4.13.2 or later, which is the vendor-released patch (pip install --upgrade 'python-engineio>=4.13.2'); the fix makes ASGI servers defer loading request bodies until the client is known, authenticated, and the payload is under the maximum allowed size, and makes Aiohttp servers enforce the max payload size in Aiohttp's WebSocket layer so oversized frames are discarded before reaching engineio. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours: Identify all systems running python-engineio ≤4.13.1, specifically those using ASGI long-polling POST or Aiohttp WebSocket configurations. …
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External POC / Exploit Code
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