Stop writing a 500 on top of a response that already started

docs/content/news.md

@@ -1,6 +1,15 @@
 <span id="news"></span>
 # Changelog
 
+## Unreleased
+
+### Bug Fixes
+
+- Worker timeout used to dump a 500 response onto a body that had already
+  started, because `sys.exit()` from the abort handler is a `BaseException`.
+  Once headers are out we just close the connection.
+  ([#3410](https://github.com/benoitc/gunicorn/issues/3410)).
+
 ## 26.2.0 - 2026-08-24
 
 ### New Features

gunicorn/workers/base_async.py

@@ -306,10 +306,10 @@ def handle_request(self, listener_name, req, sock, addr):
             # If the original exception was a socket.error we delegate
             # handling it to the caller (where handle() might ignore it)
             util.reraise(*sys.exc_info())
-        except Exception:
+        except (Exception, SystemExit):
             if resp and resp.headers_sent:
-                # If the requests have already been sent, we should close the
-                # connection to indicate the error.
+                # Timeout abort is SystemExit. If we already started the
+                # response, writing a 500 on the same socket corrupts it.
                 self.log.exception("Error handling request")
                 try:
                     sock.shutdown(socket.SHUT_RDWR)

gunicorn/workers/gthread.py

@@ -730,10 +730,10 @@ def handle_request(self, req, conn):
         except OSError:
             # pass to next try-except level
             util.reraise(*sys.exc_info())
-        except Exception:
+        except (Exception, SystemExit):
             if resp and resp.headers_sent:
-                # If the requests have already been sent, we should close the
-                # connection to indicate the error.
+                # Timeout abort is SystemExit. If we already started the
+                # response, writing a 500 on the same socket corrupts it.
                 self.log.exception("Error handling request")
                 util.close_graceful(conn.sock)
                 raise StopIteration()

gunicorn/workers/sync.py

@@ -197,10 +197,10 @@ def handle_request(self, listener, req, client, addr):
         except OSError:
             # pass to next try-except level
             util.reraise(*sys.exc_info())
-        except Exception:
+        except (Exception, SystemExit):
             if resp and resp.headers_sent:
-                # If the requests have already been sent, we should close the
-                # connection to indicate the error.
+                # Timeout abort is SystemExit. If we already started the
+                # response, writing a 500 on the same socket corrupts it.
                 self.log.exception("Error handling request")
                 util.close_graceful(client)
                 raise StopIteration()