Cache poisoning and SSRF via malformed Host headers
Published Jan 7, 2026 · Updated Jan 7, 2026
Improper Host-header validation in Undertow HTTP server core allows remote attackers to poison caches or hijack user sessions. The request path accepts absent, duplicate, malformed, or mismatched Host values instead of rejecting them, allowing downstream routing and origin logic to trust attacker-controlled authority data. No authentication is required, but exploitation requires user interaction; consequences include internal network scanning through server-side requests.
Summary
What happened
Improper Host-header validation in Undertow HTTP server core allows remote attackers to poison caches or hijack user sessions. The request path accepts absent, duplicate, malformed, or mismatched Host values instead of rejecting them, allowing downstream routing and origin logic to trust attacker-controlled authority data. No authentication is required, but exploitation requires user interaction; consequences include internal network scanning through server-side requests.
The record
- CVE
- CVE-2025-12543
- Published
- Jan 7, 2026
- Updated
- Jan 7, 2026
- Vendor
- 389 Directory Server
- Product
- Red Hat JBoss Enterprise Application Platform Expansion Pack
- Classifications
- CWE-20, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jan 7, 2026CVE publishedPublication date reported by the CVE source.
- Jan 7, 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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Public exploit references
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Technologies
Your stack
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Your stack
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