diff --git a/frigate/api/export.py b/frigate/api/export.py
index 23f975618..71aedfb11 100644
--- a/frigate/api/export.py
+++ b/frigate/api/export.py
@@ -46,6 +46,7 @@ from frigate.record.export import (
     DEFAULT_TIME_LAPSE_FFMPEG_ARGS,
     PlaybackSourceEnum,
     RecordingExporter,
+    validate_ffmpeg_args,
 )
 from frigate.util.time import is_current_hour
 
@@ -547,6 +548,24 @@ def export_recording_custom(
 
     export_id = f"{camera_name}_{''.join(random.choices(string.ascii_lowercase + string.digits, k=6))}"
 
+    # Validate user-provided ffmpeg args to prevent injection
+    for args_label, args_value in [
+        ("input", ffmpeg_input_args),
+        ("output", ffmpeg_output_args),
+    ]:
+        if args_value is not None:
+            valid, message = validate_ffmpeg_args(args_value)
+            if not valid:
+                return JSONResponse(
+                    content=(
+                        {
+                            "success": False,
+                            "message": f"Invalid ffmpeg {args_label} arguments: {message}",
+                        }
+                    ),
+                    status_code=400,
+                )
+
     # Set default values if not provided (timelapse defaults)
     if ffmpeg_input_args is None:
         ffmpeg_input_args = ""
diff --git a/frigate/record/export.py b/frigate/record/export.py
index 59a19c49c..f8a72a79a 100644
--- a/frigate/record/export.py
+++ b/frigate/record/export.py
@@ -36,6 +36,54 @@ logger = logging.getLogger(__name__)
 DEFAULT_TIME_LAPSE_FFMPEG_ARGS = "-vf setpts=0.04*PTS -r 30"
 TIMELAPSE_DATA_INPUT_ARGS = "-an -skip_frame nokey"
 
+# ffmpeg flags that can read from or write to arbitrary files
+BLOCKED_FFMPEG_ARGS = frozenset(
+    {
+        "-i",
+        "-filter_script",
+        "-vstats_file",
+        "-passlogfile",
+        "-sdp_file",
+        "-dump_attachment",
+    }
+)
+
+
+def validate_ffmpeg_args(args: str) -> tuple[bool, str]:
+    """Validate that user-provided ffmpeg args don't allow input/output injection.
+
+    Blocks:
+    - The -i flag and other flags that read/write arbitrary files
+    - Absolute/relative file paths (potential extra outputs)
+    - URLs and ffmpeg protocol references (data exfiltration)
+    """
+    if not args or not args.strip():
+        return True, ""
+
+    tokens = args.split()
+    for token in tokens:
+        # Block flags that could inject inputs or write to arbitrary files
+        if token.lower() in BLOCKED_FFMPEG_ARGS:
+            return False, f"Forbidden ffmpeg argument: {token}"
+
+        # Block tokens that look like file paths (potential output injection)
+        if (
+            token.startswith("/")
+            or token.startswith("./")
+            or token.startswith("../")
+            or token.startswith("~")
+        ):
+            return False, "File paths are not allowed in custom ffmpeg arguments"
+
+        # Block URLs and ffmpeg protocol references (e.g. http://, tcp://, pipe:, file:)
+        if "://" in token or token.startswith("pipe:") or token.startswith("file:"):
+            return (
+                False,
+                "Protocol references are not allowed in custom ffmpeg arguments",
+            )
+
+    return True, ""
+
 
 def lower_priority():
     os.nice(PROCESS_PRIORITY_LOW)