Eclipse Jetty: Cross-Request Leakage for trailers on HTTP/1.1 keep-alive connections

Description

FINDING — MEDIUM (HTTP/1.1 keep-alive connections with trailers)
HttpConnection._trailers Cross-Request Leakage (Never Reset Between Requests)

Location:
jetty-core/jetty-server/src/main/java/org/eclipse/jetty/server/internal/
HttpConnection.java:107, 1157-1161, 1170

Detail:
_trailers (line 107) is a connection-scoped HttpFields.Mutable field.
parsedTrailer() (line 1157) populates it when request N carries HTTP trailers.
messageComplete() (line 1170) checks "if (_trailers != null)" — evaluates true
from request N's data — and stamps it onto request N+1.

Grep confirms: ZERO occurrences of "_trailers = null" in entire HttpConnection.java.

Scenario:
Request N: POST /upload (trailers: X-Checksum: abc123)
Request N+1: GET /data (no trailers)
app: request.getTrailers() on N+1 → returns {X-Checksum: abc123} ← STALE

Application logic branching on getTrailers() != null produces incorrect behavior.
Not cross-connection (same keep-alive connection only).

More dangerous scenario: TOCTOU — trailer passes check, target swapped before use.

Workarounds

Do not rely on HTTP request trailers for security-sensitive logic, or disable persistent connections by closing the connection after each HTTP/1.1 request.