CVE-2023-38697 is a medium-severity (CVSS 5.8) CWE-444 vulnerability in protocol-http1. A fix is available for protocol-http1 — see the affected versions and patch details below.
protocol-http1 HTTP Request/Response Smuggling vulnerability
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2023-38697.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2023-38697 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,156 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
protocol-http1Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.
Description
Impact
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.
Patches
Fixed in protocol-http1 v0.15.1+.
Workarounds
None.
References
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | protocol-http1 | all versions | 0.15.1bundle update protocol-http1 --conservative |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for protocol-http1, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update protocol-http1 to 0.15.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-38697 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2023-38697 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2023-38697. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2023-38697 in your dependencies?
O3 Security finds CVE-2023-38697 across RubyGems dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.