protocol-http1 HTTP Request/Response Smuggling vulnerability (CVE-2023-38697)

protocol-http1 HTTP Request/Response Smuggling vulnerability (CVE-2023-38697) | HOL Guard CVE

Why this deserves its current priority

CVSS is 5.8. 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

The current feed maps protocol-http1 (rubygems). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
protocol-http1rubygems	>=0 <0.15.1	0.15.1

Recommended response

Check inventory. Check lockfiles and deployed manifests for protocol-http1.
Review the reported fix. Update protocol-http1 to 0.15.1 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Aug 3, 2023
Evidence: source:osv:source_dates:source-dates:record
Source modified
Sep 10, 2026
Evidence: source:osv:source_dates:source-dates:record
First seen by HOL
Aug 7, 2026

Sources and claim methodology

Upstream source description

### Impact [RFC 9112 Section 7.1](https://www.rfc-editor.org/rfc/rfc9112#name-chunked-transfer-coding) defined the format of chunk size, chunk data and chunk extension (detailed ABNF is in Appendix section). In summary: - The value of Content-Length header should be a string of 0-9 digits. - The chunk size should be a string of hex digits and should split from chunk data using CRLF. - The chunk extension shouldn't contain any invisible character. However, we found that Falcon has following behaviors while disobey the corresponding RFCs. - Falcon accepts Content-Length header values that have "+" prefix. - Falcon accepts Content-Length header values that written in hexadecimal with "0x" prefix. - Falcon accepts "0x" and "+" prefixed chunk size. - Falcon accepts LF in chunk extension. This behavior can lead to desync when forwarding through multiple HTTP parsers, potentially results in HTTP request smuggling and firewall bypassing. Note that while these issues were reproduced in Falcon (the server), the issue is with `protocol-http1` which implements the HTTP/1 protocol parser. We have not yet been advised of any real world exploit or practical attack. ### Patches Fixed in `protocol-http1` v0.15.1+. ### Workarounds None. ### References https://github.com/socketry/protocol-http1/pull/20

Quoted source text, attributed separately from HOL analysis.