CVE-2023-38697: protocol-http1 provides a low-level implementation of the HTTP/1 protocol. RFC 9112 Section 7.1 defined the format of chunk size, chunk data and chunk...

Description

protocol-http1 provides a low-level implementation of the HTTP/1 protocol. RFC 9112 Section 7.1 defined the format of chunk size, chunk data and chunk extension. 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, and the chunk extension shouldn't contain any invisible character. However, Falcon has following behaviors while disobey the corresponding RFCs: accepting Content-Length header values that have `+` prefix, accepting Content-Length header values that written in hexadecimal with `0x` prefix, accepting `0x` and `+` prefixed chunk size, and accepting 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. This issue is fixed in `protocol-http1` v0.15.1. There are no known workarounds.

Metrics

CVSS 3.1

5.3/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS Probability

0.64%

45.9th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-444

Affected Software

Vendor	Product	Versions
Socketry	Protocol-Http1	< 0.15.1

References

https://github.com/socketry/protocol-http1/commit/e11fc164fd2b36f7b7e785e69fa8859eb06bceddPatch
https://github.com/socketry/protocol-http1/pull/20Issue Tracking
https://github.com/socketry/protocol-http1/security/advisories/GHSA-6jwc-qr2q-7xwjVendor Advisory
https://www.rfc-editor.org/rfc/rfc9112#name-chunked-transfer-codingTechnical Description
https://github.com/socketry/protocol-http1/commit/e11fc164fd2b36f7b7e785e69fa8859eb06bceddPatch
https://github.com/socketry/protocol-http1/pull/20Issue Tracking
https://github.com/socketry/protocol-http1/security/advisories/GHSA-6jwc-qr2q-7xwjVendor Advisory
https://www.rfc-editor.org/rfc/rfc9112#name-chunked-transfer-codingTechnical Description

Timeline

Published: Aug 4, 2023
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2023-38697?

protocol-http1 provides a low-level implementation of the HTTP/1 protocol. RFC 9112 Section 7.1 defined the format of chunk size, chunk data and chunk extension. 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, and the chunk extension shouldn't contain any invisible character. However, Falcon has following behaviors while disobey the corresponding RFCs: accepting Content-Length header values that have `+` prefix, accepting Content-Length header values that written in hexadecimal with `0x` prefix, accepting `0x` and `+` prefixed chunk size, and accepting 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. This issue is fixed in `protocol-http1` v0.15.1. There are no known workarounds.

How severe is CVE-2023-38697?

CVE-2023-38697 has a CVSS score of 5.3/10 (MEDIUM severity). The EPSS model estimates a 0.64% probability of exploitation in the next 30 days.

How do I fix CVE-2023-38697?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.