Index: generic/tkImgGIF.c
===================================================================
RCS file: /cvsroot/tktoolkit/tk/generic/tkImgGIF.c,v
retrieving revision 1.24.2.5
diff -u -r1.24.2.5 tkImgGIF.c
--- generic/tkImgGIF.c	11 Sep 2007 18:01:45 -0000	1.24.2.5
+++ generic/tkImgGIF.c	25 Jan 2008 19:23:01 -0000
@@ -826,6 +826,12 @@
 		Tcl_PosixError(interp), (char *) NULL);
 	return TCL_ERROR;
     }
+
+    if (initialCodeSize > MAX_LWZ_BITS) {
+	Tcl_SetResult(interp, "malformed image", TCL_STATIC);
+	return TCL_ERROR;
+    }
+
     if (transparent != -1) {
 	cmap[transparent][CM_RED] = 0;
 	cmap[transparent][CM_GREEN] = 0;
Index: tests/imgPhoto.test
===================================================================
RCS file: /cvsroot/tktoolkit/tk/tests/imgPhoto.test,v
retrieving revision 1.15.2.5
diff -u -r1.15.2.5 imgPhoto.test
--- tests/imgPhoto.test	11 Sep 2007 18:01:46 -0000	1.15.2.5
+++ tests/imgPhoto.test	25 Jan 2008 19:23:01 -0000
@@ -681,6 +681,35 @@
     image delete $i
 }
 
+test imgPhoto-14.4 {GIF buffer overflow} -setup {
+    set i [image create photo]
+} -body {
+    # This crashes Tk up to 8.4.17 and 8.5.0
+    $i configure -data {
+	R0lGODlhCgAKAPcAAAAAAIAAAACAAICAAAAAgIAAgACAgICAgMDAwP8AAAD/
+	AP//AAAA//8A/wD//////wAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
+	AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
+	AAAAMwAAZgAAmQAAzAAA/wAzAAAzMwAzZgAzmQAzzAAz/wBmAABmMwBmZgBm
+	mQBmzABm/wCZAACZMwCZZgCZmQCZzACZ/wDMAADMMwDMZgDMmQDMzADM/wD/
+	AAD/MwD/ZgD/mQD/zAD//zMAADMAMzMAZjMAmTMAzDMA/zMzADMzMzMzZjMz
+	mTMzzDMz/zNmADNmMzNmZjNmmTNmzDNm/zOZADOZMzOZZjOZmTOZzDOZ/zPM
+	ADPMMzPMZjPMmTPMzDPM/zP/ADP/MzP/ZjP/mTP/zDP//2YAAGYAM2YAZmYA
+	mWYAzGYA/2YzAGYzM2YzZmYzmWYzzGYz/2ZmAGZmM2ZmZmZmmWZmzGZm/2aZ
+	AGaZM2aZZmaZmWaZzGaZ/2bMAGbMM2bMZmbMmWbMzGbM/2b/AGb/M2b/Zmb/
+	mWb/zGb//5kAAJkAM5kAZpkAmZkAzJkA/5kzAJkzM5kzZpkzmZkzzJkz/5lm
+	AJlmM5lmZplmmZlmzJlm/5mZAJmZM5mZZpmZmZmZzJmZ/5nMAJnMM5nMZpnM
+	mZnMzJnM/5n/AJn/M5n/Zpn/mZn/zJn//8wAAMwAM8wAZswAmcwAzMwA/8wz
+	AMwzM8wzZswzmcwzzMwz/8xmAMxmM8xmZsxmmcxmzMxm/8yZAMyZM8yZZsyZ
+	mcyZzMyZ/8zMAMzMM8zMZszMmczMzMzM/8z/AMz/M8z/Zsz/mcz/zMz///8A
+	AP8AM/8AZv8Amf8AzP8A//8zAP8zM/8zZv8zmf8zzP8z//9mAP9mM/9mZv9m
+	mf9mzP9m//+ZAP+ZM/+ZZv+Zmf+ZzP+Z///MAP/MM//MZv/Mmf/MzP/M////
+	AP//M///Zv//mf//zP///yH5BAEAABAALAAAAAAKAAoAABUSAAD/HEiwoMGD
+	CBMqXMiwYcKAADs=
+    } 
+} -cleanup {
+    image delete $i
+} -returnCodes error -result {malformed image}
+
 test imgPhoto-15.1 {photo images can fail to allocate memory gracefully} \
 	{nonPortable} {
     # This is not portable to very large machines with more around