HTTP request smuggling via underscore header confusion
Published Sep 10, 2026 · Updated Sep 10, 2026
HTTP request smuggling in Puma 5.0.0 through 8.0.2 allows remote attackers to bypass proxy request boundaries via underscore headers. The HTTP parser converts underscores in Transfer-Encoding and Content-Length names to commas, while setup_body checks only canonical environment keys. Exploitation requires a front-end proxy that accepts underscore header names and interprets request boundaries differently, enabling access-control bypass, cache poisoning, or data exposure.
Summary
What happened
HTTP request smuggling in Puma 5.0.0 through 8.0.2 allows remote attackers to bypass proxy request boundaries via underscore headers. The HTTP parser converts underscores in Transfer-Encoding and Content-Length names to commas, while setup_body checks only canonical environment keys. Exploitation requires a front-end proxy that accepts underscore header names and interprets request boundaries differently, enabling access-control bypass, cache poisoning, or data exposure.
The record
- CVE
- CVE-2026-68006
- Published
- Sep 10, 2026
- Updated
- Sep 10, 2026
- Vendor
- Unknown vendor
- Product
- Unknown product
- Classifications
- CWE-444, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Sep 10, 2026CVE publishedPublication date reported by the CVE source.
- Sep 10, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
Compare your product and version with the public record. A matching version still requires validation against your environment.
Is a vulnerable build present?
What conditions does exploitation require?
What is affected?
Affected products and versions are unavailable in this record.
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Underscore-header request-smuggling proof of conceptproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
See the directory against your own environment.
Your stack
Check the software in your environment
Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.
Book a demo