diff --git a/backend/app/routers/file_config.py b/backend/app/routers/file_config.py
index 43fd808..57a199d 100644
--- a/backend/app/routers/file_config.py
+++ b/backend/app/routers/file_config.py
@@ -6,6 +6,7 @@ files directly on the filesystem (``jail.d/``, ``filter.d/``, ``action.d/``).
 Endpoints:
 * ``GET  /api/config/jail-files``                  — list all jail config files
 * ``GET  /api/config/jail-files/{filename}``        — get one jail config file (with content)
+* ``PUT  /api/config/jail-files/{filename}``        — overwrite a jail config file
 * ``PUT  /api/config/jail-files/{filename}/enabled`` — enable/disable a jail config
 * ``GET  /api/config/filters``                     — list all filter files
 * ``GET  /api/config/filters/{name}``              — get one filter file (with content)
@@ -169,6 +170,46 @@ async def get_jail_config_file(
         raise _service_unavailable(str(exc)) from exc
 
 
+@router.put(
+    "/jail-files/{filename}",
+    status_code=status.HTTP_204_NO_CONTENT,
+    summary="Overwrite a jail.d config file with new raw content",
+)
+async def write_jail_config_file(
+    request: Request,
+    _auth: AuthDep,
+    filename: _FilenamePath,
+    body: ConfFileUpdateRequest,
+) -> None:
+    """Overwrite the raw content of an existing jail.d config file.
+
+    The change is written directly to disk.  You must reload fail2ban
+    (``POST /api/config/reload``) separately for the change to take effect.
+
+    Args:
+        request: Incoming request.
+        _auth: Validated session.
+        filename: Filename of the jail config file (e.g. ``sshd.conf``).
+        body: New raw file content.
+
+    Raises:
+        HTTPException: 400 if *filename* is unsafe or content is invalid.
+        HTTPException: 404 if the file does not exist.
+        HTTPException: 503 if the config directory is unavailable.
+    """
+    config_dir: str = request.app.state.settings.fail2ban_config_dir
+    try:
+        await file_config_service.write_jail_config_file(config_dir, filename, body)
+    except ConfigFileNameError as exc:
+        raise _bad_request(str(exc)) from exc
+    except ConfigFileNotFoundError:
+        raise _not_found(filename) from None
+    except ConfigFileWriteError as exc:
+        raise _bad_request(str(exc)) from exc
+    except ConfigDirError as exc:
+        raise _service_unavailable(str(exc)) from exc
+
+
 @router.put(
     "/jail-files/{filename}/enabled",
     status_code=status.HTTP_204_NO_CONTENT,
diff --git a/backend/app/services/file_config_service.py b/backend/app/services/file_config_service.py
index ad0462a..271cbc8 100644
--- a/backend/app/services/file_config_service.py
+++ b/backend/app/services/file_config_service.py
@@ -418,6 +418,49 @@ async def create_jail_config_file(
     return await asyncio.get_event_loop().run_in_executor(None, _do)
 
 
+async def write_jail_config_file(
+    config_dir: str,
+    filename: str,
+    req: ConfFileUpdateRequest,
+) -> None:
+    """Overwrite an existing jail.d config file with new raw content.
+
+    Args:
+        config_dir: Path to the fail2ban configuration directory.
+        filename: Filename including extension (e.g. ``sshd.conf``).
+        req: :class:`~app.models.file_config.ConfFileUpdateRequest` with new
+            content.
+
+    Raises:
+        ConfigFileNotFoundError: If the file does not exist.
+        ConfigFileNameError: If *filename* is unsafe or has a bad extension.
+        ConfigFileWriteError: If the file cannot be written.
+        ConfigDirError: If *config_dir* does not exist.
+    """
+
+    def _do() -> None:
+        jail_d = _resolve_subdir(config_dir, "jail.d").resolve()
+        if not jail_d.is_dir():
+            raise ConfigFileNotFoundError(filename)
+        path = (jail_d / filename).resolve()
+        _assert_within(jail_d, path)
+        if path.suffix not in _CONF_EXTENSIONS:
+            raise ConfigFileNameError(
+                f"Only .conf and .local files are supported, got {filename!r}."
+            )
+        if not path.is_file():
+            raise ConfigFileNotFoundError(filename)
+        try:
+            path.write_text(req.content, encoding="utf-8")
+        except OSError as exc:
+            raise ConfigFileWriteError(
+                f"Cannot write {filename!r}: {exc}"
+            ) from exc
+        log.info("jail_config_file_written", filename=filename)
+
+    await asyncio.get_event_loop().run_in_executor(None, _do)
+
+
 # ---------------------------------------------------------------------------
 # Internal helpers — generic conf file listing / reading / writing
 # ---------------------------------------------------------------------------