CVE-2026-12606 in Grizzly
Summary
by MITRE • 07/14/2026
Eclipse Grizzly in versions before 5.0.2, cannot properly parse the trailer section in malformed trailer header's line, which can be leveraged to perform HTTP request smuggling.
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Analysis
by VulDB Data Team • 07/14/2026
The vulnerability exists within Eclipse Grizzly web server components prior to version 5.0.2 where the HTTP parser fails to properly handle malformed trailer headers in HTTP requests. This parsing inconsistency creates a potential pathway for HTTP request smuggling attacks by allowing attackers to manipulate the trailer section of HTTP messages. The flaw specifically manifests when processing HTTP requests containing malformed trailer header lines, which can cause the server to incorrectly interpret the message boundaries and potentially process multiple requests within a single connection. Such vulnerabilities fall under CWE-1247 which addresses improper handling of HTTP headers and trailers in web servers. The issue enables adversaries to exploit the inconsistent parsing behavior to craft malicious requests that may bypass security controls or manipulate server processing logic.
The technical exploitation of this vulnerability relies on the server's inability to correctly parse trailer sections within HTTP messages, particularly when these trailers contain malformed data structures. When a maliciously crafted HTTP request reaches the Grizzly server, the parser encounters unexpected trailer content and fails to properly segment the message boundaries. This parsing failure can result in the server treating parts of subsequent requests as part of the current request, effectively allowing attackers to smuggle requests through the server infrastructure. The vulnerability is particularly concerning because it operates at the HTTP protocol level and can be leveraged to bypass various security mechanisms including authentication checks, access controls, and content filtering systems. Attackers can construct requests where the trailer section contains data that causes the parser to skip over legitimate request boundaries, creating opportunities for request manipulation.
The operational impact of this vulnerability extends beyond simple parsing errors and can enable sophisticated attacks against web applications relying on Grizzly servers. An attacker could potentially leverage HTTP request smuggling to perform cross-site scripting attacks by injecting malicious payloads into subsequent requests, or manipulate server-side processing to bypass security controls. The vulnerability also poses risks to application logic that depends on proper HTTP message boundaries, as the malformed trailer handling can cause unexpected behavior in applications that process HTTP data streams. Organizations using Grizzly servers in production environments face potential exposure to data leakage, unauthorized access, and service disruption if this vulnerability remains unpatched. The issue aligns with ATT&CK technique T1071.004 which covers application layer protocol manipulation and can be used to establish persistent access or escalate privileges within compromised systems.
Mitigation strategies should prioritize immediate patching of affected Grizzly versions to 5.0.2 or later where the trailer parsing logic has been corrected. Organizations should also implement network-level monitoring to detect unusual HTTP request patterns that may indicate smuggling attempts, particularly focusing on malformed trailer headers and unexpected message boundaries. Additional defensive measures include implementing strict HTTP protocol validation at proxy layers, configuring web application firewalls to block suspicious trailer content, and conducting regular security assessments of HTTP handling components. The fix implemented in version 5.0.2 addresses the core parsing logic to ensure proper handling of trailer sections while maintaining compatibility with legitimate HTTP requests. Security teams should also consider implementing automated vulnerability scanning to identify other potential parsing inconsistencies within their web server infrastructure and establish incident response procedures for detecting and responding to exploitation attempts targeting HTTP protocol vulnerabilities.