diff --git a/TODO.md b/TODO.md
index 95414b3..fd125d4 100644
--- a/TODO.md
+++ b/TODO.md
@@ -157,13 +157,13 @@ A single linear checklist of tasks to implement the complete pixa caching image
 - [x] Implement image resizing with size options (WxH, 0x0, orig)
 - [x] Implement format conversion (JPEG, PNG, WebP, AVIF)
 - [x] Implement quality parameter support
-- [ ] Implement max input dimensions validation
-- [ ] Implement max output dimensions validation
+- [x] Implement max input dimensions validation
+- [x] Implement max output dimensions validation
 - [ ] Implement EXIF/metadata stripping
 - [x] Implement fit modes (cover, contain, fill, inside, outside)
 
 ## Security
-- [ ] Implement path traversal prevention
+- [x] Implement path traversal prevention
 - [ ] Implement request sanitization
 - [ ] Implement response header sanitization
 - [ ] Implement referer blacklist
diff --git a/internal/imgcache/processor.go b/internal/imgcache/processor.go
index 7ce8721..cf629ad 100644
--- a/internal/imgcache/processor.go
+++ b/internal/imgcache/processor.go
@@ -3,6 +3,7 @@ package imgcache
 import (
 	"bytes"
 	"context"
+	"errors"
 	"fmt"
 	"image"
 	"image/gif"
@@ -14,6 +15,13 @@ import (
 	"golang.org/x/image/webp"
 )
 
+// MaxInputDimension is the maximum allowed width or height for input images.
+// Images larger than this are rejected to prevent DoS via decompression bombs.
+const MaxInputDimension = 8192
+
+// ErrInputTooLarge is returned when input image dimensions exceed MaxInputDimension.
+var ErrInputTooLarge = errors.New("input image dimensions exceed maximum")
+
 // ImageProcessor implements the Processor interface using pure Go libraries.
 type ImageProcessor struct{}
 
@@ -45,6 +53,11 @@ func (p *ImageProcessor) Process(
 	origWidth := bounds.Dx()
 	origHeight := bounds.Dy()
 
+	// Validate input dimensions to prevent DoS via decompression bombs
+	if origWidth > MaxInputDimension || origHeight > MaxInputDimension {
+		return nil, ErrInputTooLarge
+	}
+
 	// Determine target dimensions
 	targetWidth := req.Size.Width
 	targetHeight := req.Size.Height
diff --git a/internal/imgcache/processor_test.go b/internal/imgcache/processor_test.go
index 209fd93..135ca80 100644
--- a/internal/imgcache/processor_test.go
+++ b/internal/imgcache/processor_test.go
@@ -240,3 +240,74 @@ func TestImageProcessor_SupportedFormats(t *testing.T) {
 		t.Error("SupportedOutputFormats() returned empty slice")
 	}
 }
+
+func TestImageProcessor_RejectsOversizedInput(t *testing.T) {
+	proc := NewImageProcessor()
+	ctx := context.Background()
+
+	// Create an image that exceeds MaxInputDimension (e.g., 10000x100)
+	// This should be rejected before processing to prevent DoS
+	input := createTestJPEG(t, 10000, 100)
+
+	req := &ImageRequest{
+		Size:    Size{Width: 100, Height: 100},
+		Format:  FormatJPEG,
+		Quality: 85,
+		FitMode: FitCover,
+	}
+
+	_, err := proc.Process(ctx, bytes.NewReader(input), req)
+	if err == nil {
+		t.Error("Process() should reject oversized input images")
+	}
+
+	if err != ErrInputTooLarge {
+		t.Errorf("Process() error = %v, want ErrInputTooLarge", err)
+	}
+}
+
+func TestImageProcessor_RejectsOversizedInputHeight(t *testing.T) {
+	proc := NewImageProcessor()
+	ctx := context.Background()
+
+	// Create an image with oversized height
+	input := createTestJPEG(t, 100, 10000)
+
+	req := &ImageRequest{
+		Size:    Size{Width: 100, Height: 100},
+		Format:  FormatJPEG,
+		Quality: 85,
+		FitMode: FitCover,
+	}
+
+	_, err := proc.Process(ctx, bytes.NewReader(input), req)
+	if err == nil {
+		t.Error("Process() should reject oversized input images")
+	}
+
+	if err != ErrInputTooLarge {
+		t.Errorf("Process() error = %v, want ErrInputTooLarge", err)
+	}
+}
+
+func TestImageProcessor_AcceptsMaxDimensionInput(t *testing.T) {
+	proc := NewImageProcessor()
+	ctx := context.Background()
+
+	// Create an image at exactly MaxInputDimension - should be accepted
+	// Using smaller dimensions to keep test fast
+	input := createTestJPEG(t, MaxInputDimension, 100)
+
+	req := &ImageRequest{
+		Size:    Size{Width: 100, Height: 100},
+		Format:  FormatJPEG,
+		Quality: 85,
+		FitMode: FitCover,
+	}
+
+	result, err := proc.Process(ctx, bytes.NewReader(input), req)
+	if err != nil {
+		t.Fatalf("Process() should accept images at MaxInputDimension, got error: %v", err)
+	}
+	defer result.Content.Close()
+}
diff --git a/internal/imgcache/urlparser.go b/internal/imgcache/urlparser.go
index 30c9356..ec69d9c 100644
--- a/internal/imgcache/urlparser.go
+++ b/internal/imgcache/urlparser.go
@@ -3,6 +3,7 @@ package imgcache
 import (
 	"errors"
 	"fmt"
+	"net/url"
 	"regexp"
 	"strconv"
 	"strings"
@@ -16,6 +17,7 @@ var (
 	ErrInvalidSize       = errors.New("invalid size format")
 	ErrInvalidFormat     = errors.New("invalid or unsupported format")
 	ErrDimensionTooLarge = errors.New("dimension exceeds maximum")
+	ErrPathTraversal     = errors.New("path traversal detected")
 )
 
 // MaxDimension is the maximum allowed width or height.
@@ -73,6 +75,11 @@ func ParseImageURL(urlPath string) (*ParsedURL, error) {
 
 // parseImageComponents parses <host>/<path>/<size>.<format> structure.
 func parseImageComponents(remainder string) (*ParsedURL, error) {
+	// Check for path traversal before any other processing
+	if err := checkPathTraversal(remainder); err != nil {
+		return nil, err
+	}
+
 	// Find the last path segment which contains size.format
 	lastSlash := strings.LastIndex(remainder, "/")
 	if lastSlash == -1 {
@@ -130,6 +137,64 @@ func parseImageComponents(remainder string) (*ParsedURL, error) {
 	}, nil
 }
 
+// checkPathTraversal detects path traversal attempts in a URL path.
+// It checks for various attack vectors including:
+// - Direct ../ sequences
+// - URL-encoded variants (%2e%2e, %252e%252e)
+// - Backslash variants (..\)
+// - Null byte injection (%00)
+func checkPathTraversal(path string) error {
+	// First, URL-decode the path to catch encoded attacks
+	// Decode multiple times to catch double-encoding
+	decoded := path
+	for range 3 {
+		newDecoded, err := url.PathUnescape(decoded)
+		if err != nil {
+			// Malformed encoding is suspicious
+			return ErrPathTraversal
+		}
+
+		if newDecoded == decoded {
+			break
+		}
+
+		decoded = newDecoded
+	}
+
+	// Normalize backslashes to forward slashes
+	normalized := strings.ReplaceAll(decoded, "\\", "/")
+
+	// Check for null bytes
+	if strings.Contains(normalized, "\x00") {
+		return ErrPathTraversal
+	}
+
+	// Check for parent directory traversal
+	// Look for "/.." or "../" patterns
+	if strings.Contains(normalized, "/../") ||
+		strings.Contains(normalized, "/..") ||
+		strings.HasPrefix(normalized, "../") ||
+		strings.HasSuffix(normalized, "/..") ||
+		normalized == ".." {
+		return ErrPathTraversal
+	}
+
+	// Also check for ".." as a path segment in the original path
+	// This catches cases where the path hasn't been normalized
+	segments := strings.Split(path, "/")
+	for _, seg := range segments {
+		// URL decode the segment
+		decodedSeg, _ := url.PathUnescape(seg)
+		decodedSeg = strings.ReplaceAll(decodedSeg, "\\", "/")
+
+		if decodedSeg == ".." {
+			return ErrPathTraversal
+		}
+	}
+
+	return nil
+}
+
 // parseSizeFormat parses strings like "800x600.webp" or "orig.png"
 func parseSizeFormat(s string) (Size, ImageFormat, error) {
 	matches := sizeFormatRegex.FindStringSubmatch(s)
diff --git a/internal/imgcache/urlparser_test.go b/internal/imgcache/urlparser_test.go
index a7cf141..bcfc61f 100644
--- a/internal/imgcache/urlparser_test.go
+++ b/internal/imgcache/urlparser_test.go
@@ -247,6 +247,94 @@ func TestParsedURL_ToImageRequest(t *testing.T) {
 	}
 }
 
+func TestParseImageURL_PathTraversal(t *testing.T) {
+	// All path traversal attempts should be rejected
+	tests := []struct {
+		name  string
+		input string
+	}{
+		{
+			name:  "simple parent directory",
+			input: "/v1/image/cdn.example.com/../etc/passwd/800x600.jpeg",
+		},
+		{
+			name:  "double parent directory",
+			input: "/v1/image/cdn.example.com/../../etc/passwd/800x600.jpeg",
+		},
+		{
+			name:  "parent in middle of path",
+			input: "/v1/image/cdn.example.com/photos/../../../etc/passwd/800x600.jpeg",
+		},
+		{
+			name:  "encoded parent directory",
+			input: "/v1/image/cdn.example.com/photos/%2e%2e/secret/800x600.jpeg",
+		},
+		{
+			name:  "double encoded parent",
+			input: "/v1/image/cdn.example.com/photos/%252e%252e/secret/800x600.jpeg",
+		},
+		{
+			name:  "backslash traversal",
+			input: "/v1/image/cdn.example.com/photos/..\\secret/800x600.jpeg",
+		},
+		{
+			name:  "mixed slashes",
+			input: "/v1/image/cdn.example.com/photos/../\\../secret/800x600.jpeg",
+		},
+		{
+			name:  "null byte injection",
+			input: "/v1/image/cdn.example.com/photos/image.jpg%00.png/800x600.jpeg",
+		},
+		{
+			name:  "parent at start of path",
+			input: "/v1/image/cdn.example.com/../800x600.jpeg",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			_, err := ParseImageURL(tt.input)
+			if err == nil {
+				t.Error("ParseImageURL() should reject path traversal attempts")
+			}
+
+			if err != ErrPathTraversal {
+				t.Errorf("ParseImageURL() error = %v, want ErrPathTraversal", err)
+			}
+		})
+	}
+}
+
+func TestParseImagePath_PathTraversal(t *testing.T) {
+	// Test path traversal via ParseImagePath (chi wildcard)
+	tests := []struct {
+		name  string
+		input string
+	}{
+		{
+			name:  "parent directory in path",
+			input: "cdn.example.com/photos/../secret/800x600.jpeg",
+		},
+		{
+			name:  "encoded traversal",
+			input: "cdn.example.com/photos/%2e%2e/secret/800x600.jpeg",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			_, err := ParseImagePath(tt.input)
+			if err == nil {
+				t.Error("ParseImagePath() should reject path traversal attempts")
+			}
+
+			if err != ErrPathTraversal {
+				t.Errorf("ParseImagePath() error = %v, want ErrPathTraversal", err)
+			}
+		})
+	}
+}
+
 // errorIs checks if err matches target (handles wrapped errors).
 func errorIs(err, target error) bool {
 	if err == target {