Host Header Injection in Undertow HTTP Server Core
CVE-2025-12543 is a critical input validation flaw in the Undertow HTTP server core used by WildFly, JBoss EAP, and other Java applications. Undertow fails to properly validate the HTTP Host header in incoming requests and accepts malformed or attacker-controlled Host values instead of rejecting them. This creates a Host header injection condition in which application logic, generated links, cache keys, or downstream components may trust and process unvalidated host information. Reported abuse scenarios include web cache poisoning, SSRF-style/internal network reconnaissance, and session hijacking. The issue is described as remotely exploitable without authentication, and affected deployments include Undertow-based applications and platform distributions such as WildFly and JBoss EAP that embed vulnerable Undertow components.
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Impact, mitigation & remediation
What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
Impact
What an attacker gets, and what they’ve been doing with it.
Mitigation
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Remediation
Patch, then assume compromise.
Exploits
No valid public exploits. Mallory filtered out 1 candidate as fakes, detection scripts, or README-only repos.
All candidate exploits were filtered out by Mallory's validation.
Affected products & vendors
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
Recent activity
19 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
Unknown (listed as a trending CVE affecting HPE Telco Service Activator).
Unknown (listed as a trending CVE affecting HPE Telco Service Activator; no technical details provided in the content).
A critical improper input validation vulnerability in Undertow HTTP server core, allowing attackers to exploit malformed Host headers for session hijacking, cache poisoning, and internal network compromise.
A critical Host header injection vulnerability in the Undertow Java web server core that allows malicious Host header values to be processed, enabling impacts such as cache poisoning, internal network probing (SSRF-style), and session hijacking; remotely exploitable without authentication.
The version that knows your environment.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.