Request smuggling via stripped leading header whitespace
Published Mar 27, 2026 · Updated Mar 27, 2026
HTTP request smuggling in Undertow allows remote attackers to bypass front-end controls via a malformed first header line. Undertow's HTTP parser strips leading spaces from an invalid first field-line instead of rejecting the request, causing intermediaries and the back end to disagree on message boundaries. Exploitation requires a front end that parses the request differently; it enables unauthorized request routing, restricted-data access, or cache manipulation without affecting availability.
Summary
What happened
HTTP request smuggling in Undertow allows remote attackers to bypass front-end controls via a malformed first header line. Undertow's HTTP parser strips leading spaces from an invalid first field-line instead of rejecting the request, causing intermediaries and the back end to disagree on message boundaries. Exploitation requires a front end that parses the request differently; it enables unauthorized request routing, restricted-data access, or cache manipulation without affecting availability.
The record
- CVE
- CVE-2026-28369
- Published
- Mar 27, 2026
- Updated
- Mar 27, 2026
- Vendor
- 389 Directory Server
- Product
- Red Hat JBoss Enterprise Application Platform Expansion Pack
- Classifications
- CWE-444, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Mar 27, 2026CVE publishedPublication date reported by the CVE source.
- Mar 27, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Affected versions are unavailable in this record. Check the vendor advisory for version and patch details.
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
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Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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