CVE-2023-38697

protocol-http1 HTTP Request/Response Smuggling vulnerability

Workarounds

None.

References

https://github.com/socketry/protocol-http1/pull/20

RFC 9112 Section 7.1 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.

CVE-2023-38697 has a CVSS score of 5.8 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.15.1); upgrading removes the vulnerable code path.

Kodem intelligence

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Fixed in protocol-http1 v0.15.1+.

1. What is CVE-2023-38697? CVE-2023-38697 is a medium-severity security vulnerability in protocol-http1 (rubygems), affecting versions < 0.15.1. It is fixed in 0.15.1.
2. How severe is CVE-2023-38697? CVE-2023-38697 has a CVSS score of 5.8 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of protocol-http1 are affected by CVE-2023-38697? protocol-http1 (rubygems) versions < 0.15.1 is affected.
4. Is there a fix for CVE-2023-38697? Yes. CVE-2023-38697 is fixed in 0.15.1. Upgrade to this version or later.
5. Is CVE-2023-38697 exploitable, and should I be worried? Whether CVE-2023-38697 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2023-38697 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2023-38697? Upgrade protocol-http1 to 0.15.1 or later.