GHSA-FCR3-V77C-X7HX
Vulnerability from github – Published: 2026-09-18 12:31 – Updated: 2026-09-18 15:32Summary
Netty's fix for CVE-2026-44248 is incomplete. The decoder checks if the MQTT packet's Remaining Length exceeds maxBytesInMessage, but fails to validate the Properties Length against the Remaining Length. An attacker can bypass the size limit by sending a small Remaining Length but an enormous Properties Length. This forces Netty to buffer and parse millions of properties, allowing an unauthenticated remote attacker to trigger excessive memory and CPU consumption, leading to OutOfMemoryError.
Details
In io.netty.handler.codec.mqtt.MqttDecoder, the decodeProperties() helper method reads totalPropertiesLength and attempts to parse that many bytes. If the buffer lacks the full length, a Signal is thrown. The catch block inside decode() only enforces maxBytesInMessage against bytesRemainingBeforeVariableHeader (the packet's Remaining Length).
By sending a CONNECT packet with a small Remaining Length but a huge Properties Length, the size check passes. ReplayingDecoder then buffers data from the network until the huge Properties Length is reached, parsing millions of UserProperty objects and exhausting CPU and memory.
{
"affected": [],
"aliases": [
"CVE-2026-93575"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-18T11:17:22Z",
"severity": "HIGH"
},
"details": "### Summary\nNetty\u0027s fix for CVE-2026-44248 is incomplete. The decoder checks if the MQTT packet\u0027s `Remaining Length` exceeds `maxBytesInMessage`, but fails to validate the `Properties Length` against the `Remaining Length`. An attacker can bypass the size limit by sending a small `Remaining Length` but an enormous `Properties Length`. This forces Netty to buffer and parse millions of properties, allowing an unauthenticated remote attacker to trigger excessive memory and CPU consumption, leading to OutOfMemoryError.\n\n### Details\nIn `io.netty.handler.codec.mqtt.MqttDecoder`, the `decodeProperties()` helper method reads `totalPropertiesLength` and attempts to parse that many bytes. If the buffer lacks the full length, a `Signal` is thrown. The `catch` block inside `decode()` only enforces `maxBytesInMessage` against `bytesRemainingBeforeVariableHeader` (the packet\u0027s `Remaining Length`).\n\nBy sending a `CONNECT` packet with a small `Remaining Length` but a huge `Properties Length`, the size check passes. `ReplayingDecoder` then buffers data from the network until the huge `Properties Length` is reached, parsing millions of `UserProperty` objects and exhausting CPU and memory.\n\n#",
"id": "GHSA-fcr3-v77c-x7hx",
"modified": "2026-09-18T15:32:15Z",
"published": "2026-09-18T12:31:20Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-93575"
},
{
"type": "WEB",
"url": "https://access.redhat.com/security/cve/CVE-2026-93575"
},
{
"type": "WEB",
"url": "https://bugzilla.redhat.com/show_bug.cgi?id=2536967"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
]
}
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