Io.netty/netty-codec-http: netty: http request smuggling due to control characters in the chunk-size line (CVE-2026-93566) | HOL Guard CVE

Unknown severity · Source severity not reportedCVE-2026-93566

Io.netty/netty-codec-http: netty: http request smuggling due to control characters in the chunk-size line

Answer in brief

CVE-2026-93566 records a Unknown severity vulnerability in Io.netty/netty-codec-http: netty: http request smuggling due to control characters in the chunk-size line. The current sources do not mark it as known exploited. Affected software not mapped in the current feed; confirm the named product and version against your inventory.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 18, 2026Updated Sep 18, 2026Source checked Sep 18, 2026First seen by HOL Sep 18, 2026Material review Sep 18, 2026

Upstream Advisory

Key facts

Risk: Unknown severitySource severity not reported
Exploitation: Not marked as known exploited
Affected software: Not mapped
Fix availability: Not reported

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

Affected software not mapped in the current feed; confirm the named product and version against your inventory.

Recommended response

Confirm exposure. Identify whether the named product or interface exists in your inventory, then review the linked upstream references for affected versions and vendor guidance.

Evidence timeline and material changes

Published upstream
Sep 18, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 18, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 18, 2026

Sources and claim methodology

Upstream source description

### Summary 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: ```java 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

Quoted source text, attributed separately from HOL analysis.