diff --git a/services/tiktak/server/server.go b/services/tiktak/server/server.go
index ea818a3..b7f2e2d 100644
--- a/services/tiktak/server/server.go
+++ b/services/tiktak/server/server.go
@@ -23,6 +23,10 @@ func NewServer(db *db.Storage, vs *video.Storage, c Config) *Server {
 	t := Template{template.Must(template.ParseGlob(c.TemplatesFolder + "/*.html"))}
 	s.e.Renderer = &t
 	s.e.Use(middleware.Recover())
+	// Hard cap on the whole request. The video file is size-checked separately,
+	// but nothing bounded the form fields: a huge subtitles blob becomes one
+	// slice entry per line inside GenerateVtt.
+	s.e.Use(middleware.BodyLimit("8M"))
 	s.e.Use(func(next echo.HandlerFunc) echo.HandlerFunc {
 		return func(c echo.Context) error {
 			cc := &auth.Context{Context: c}
@@ -111,6 +115,9 @@ func (s *Server) handleCreate(c echo.Context) error {
 
 	descr := c.FormValue("description")
 	subt := c.FormValue("subtitles")
+	if len(subt) > video.MaxSubtitlesSize {
+		return c.Render(http.StatusUnprocessableEntity, "create", ErrorResponse{"subtitles are too long"})
+	}
 	isPrivate := c.FormValue("private")
 	v := db.Video{UserID: uid, Description: descr, Private: isPrivate == "on", Link: link}
 
diff --git a/services/tiktak/video/preview.go b/services/tiktak/video/preview.go
index db731d2..32b6b04 100644
--- a/services/tiktak/video/preview.go
+++ b/services/tiktak/video/preview.go
@@ -6,6 +6,7 @@ import (
 	"github.com/disintegration/imaging"
 	"image"
 	"image/png"
+	"io"
 	"os"
 	"os/exec"
 	"strings"
@@ -14,11 +15,17 @@ import (
 
 var (
 	ProcessingDeadline = 2 * time.Second
-	semaphore          = make(chan struct{}, 75)
+	// 75 concurrent ffmpeg processes are enough to swap the box out on their
+	// own, bomb or no bomb.
+	semaphore = make(chan struct{}, 16)
 )
 
 func generatePreview(ctx context.Context, inp string, out string) error {
-	cmd := exec.CommandContext(ctx, "ffmpeg", "-y", "-i", inp, "-vframes", "1", out)
+	// Reject decompression bombs before ffmpeg expands a frame into memory.
+	if err := checkGeometry(ctx, inp); err != nil {
+		return err
+	}
+	cmd := exec.CommandContext(ctx, "ffmpeg", "-y", "-threads", "1", "-i", inp, "-vframes", "1", out)
 	s := strings.Builder{}
 	cmd.Stdout = &s
 	cmd.Stderr = &s
@@ -48,6 +55,21 @@ func Blur(inp string, out string) error {
 	if err != nil {
 		return err
 	}
+	defer f.Close()
+
+	// Same guard on the decode side: imaging.Blur keeps several copies of the
+	// bitmap alive, so an oversized preview is an OOM all by itself.
+	cfg, _, err := image.DecodeConfig(f)
+	if err != nil {
+		return err
+	}
+	if cfg.Width*cfg.Height > MaxPixels {
+		return fmt.Errorf("preview %dx%d is too large to blur", cfg.Width, cfg.Height)
+	}
+	if _, err := f.Seek(0, io.SeekStart); err != nil {
+		return err
+	}
+
 	img, _, err := image.Decode(f)
 	if err != nil {
 		return err
diff --git a/services/tiktak/video/probe.go b/services/tiktak/video/probe.go
new file mode 100644
index 0000000..b73b579
--- /dev/null
+++ b/services/tiktak/video/probe.go
@@ -0,0 +1,36 @@
+package video
+
+import (
+	"context"
+	"fmt"
+	"os/exec"
+	"strings"
+)
+
+// Decompression-bomb guard. A 100 KB webm can carry a 16383x16383 VP8 frame
+// (the format's maximum): tiny on disk, ~1 GB once ffmpeg expands it to raw
+// pixels. Probing the container header is cheap -- ffprobe reads metadata and
+// never decodes a frame -- so we reject absurd geometry before any decoding.
+const (
+	MaxDimension = 4096
+	MaxPixels    = 8 << 20 // 8 Mpx, ~4x a 1080p frame
+)
+
+func checkGeometry(ctx context.Context, inp string) error {
+	args := []string{"-v", "error", "-select_streams", "v:0",
+		"-show_entries", "stream=width,height", "-of", "csv=s=x:p=0", inp}
+
+	out, err := exec.CommandContext(ctx, "ffprobe", args...).Output()
+	if err != nil {
+		return fmt.Errorf("cannot probe video: %v", err)
+	}
+
+	var w, h int
+	if _, err := fmt.Sscanf(strings.TrimSpace(string(out)), "%dx%d", &w, &h); err != nil {
+		return fmt.Errorf("cannot read video geometry")
+	}
+	if w <= 0 || h <= 0 || w > MaxDimension || h > MaxDimension || w*h > MaxPixels {
+		return fmt.Errorf("video resolution %dx%d is not supported", w, h)
+	}
+	return nil
+}
diff --git a/services/tiktak/video/storage.go b/services/tiktak/video/storage.go
index f9dfc82..2d8ad82 100644
--- a/services/tiktak/video/storage.go
+++ b/services/tiktak/video/storage.go
@@ -12,6 +12,9 @@ import (
 
 const (
 	MaxSize = 5 << 20
+
+	// GenerateVtt splits this on \n and allocates one slice entry per line.
+	MaxSubtitlesSize = 64 << 10
 )
 
 var (