Eclipse Grizzly CVE-2026-12606

Exploitation is most effective when GlassFish with a vulnerable Grizzly version is deployed behind a reverse proxy or load balancer (e.g., nginx, HAProxy, Apache httpd) that forwards HTTP/1.1 chunked requests - this is the architectural condition implied by the CVSS 4.0 AT:P (Attack Requirements: Present) flag. The attacker must be able to send HTTP/1.1 requests with chunked transfer-encoding and a trailer section containing a malformed header line; standard non-chunked requests are not affected. No authentication is required (PR:N in CVSS vector). Exploitation is limited by the need for the proxy and Grizzly to parse the malformed trailer boundary differently; in direct-access deployments without a proxy, the smuggling primitive is weakened, though parser anomalies may still occur. No specific non-default configuration option is documented as a prerequisite.

The CVSS 4.0 score of 6.3 with vector AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N reflects network reachability without authentication, but the AT:P (Attack Requirements: Present) flag depresses the score significantly - effective HTTP request smuggling requires a specific intermediary topology (a proxy or load balancer in the request path that interprets chunked trailers differently from Grizzly). The 'Information Disclosure' tag in the intelligence data is in mild tension with VC:N in the CVSS vector; request smuggling can enable session hijacking and response poisoning that yields confidentiality impact in practice, but this is not formally reflected in the provided scoring. The absence of KEV listing and any POC reference suggests no active or widespread exploitation at time of analysis. Real-world priority is highest for GlassFish deployments behind a reverse proxy handling untrusted chunked HTTP/1.1 traffic; deployments where GlassFish is directly internet-exposed without a proxy reduce the smuggling vector but retain the parser anomaly. EPSS data was not provided in the input - exploitation probability cannot be quantified.

An unauthenticated attacker sends a crafted HTTP/1.1 request with chunked transfer-encoding and a deliberately malformed trailer header line to a reverse proxy fronting a GlassFish server. The proxy treats the entire payload as one request and forwards it, while Grizzly - due to the parser flaw - splits it into two at the malformed trailer boundary. The second, attacker-crafted segment is then processed by GlassFish as the opening of the next legitimate user's request, allowing the attacker to prepend arbitrary HTTP content to that user's session, potentially hijacking authentication tokens or invoking privileged endpoints on their behalf.