CVE-2016-5116 (published 2016-08-07T10:59Z)

gd_xbm.c in the GD Graphics Library (aka libgd) before 2.2.0, as used in certain custom PHP 5.5.x configurations, allows context-dependent attackers to obtain sensitive information from process memory or cause a denial of service (stack-based buffer under-read and application crash) via a long name.

Severity: MEDIUM
CVSS v2 base score: 6.4 (AV:N/AC:L/Au:N/C:P/I:N/A:P)
CVSS v3 base score: 9.1, CRITICAL (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H)

Weakness information:
cwe_id: CWE-119
cwe_name: Improper Restriction of Operations within the Bounds of a Memory Buffer
description: The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.
extended_description: 
            Certain languages allow direct addressing of memory locations and do not automatically ensure that these locations are valid for the memory buffer that is being referenced. This can cause read or write operations to be performed on memory locations that may be associated with other variables, data structures, or internal program data.
         
         

Fix information:
repo_url: https://github.com/libgd/libgd
commit_details: repo_url: https://github.com/libgd/libgd
author: Mike Frysinger
author_date: 2016-05-14 01:38:18-04:00
msg: xbm: avoid stack overflow (read) with large names #211

We use the name passed in to printf into a local stack buffer which is
limited to 4000 bytes.  So given a large enough value, lots of stack
data is leaked.  Rewrite the code to do simple memory copies with most
of the strings to avoid that issue, and only use stack buffer for small
numbers of constant size.

This closes #211.
repository: repo_url: https://github.com/libgd/libgd
repo_name: libgd/libgd
description: GD Graphics Library
repo_language: C
owner: libgd
file_changes: filename: gd_xbm.c
change_type: ModificationType.MODIFY
diff: @@ -180,7 +180,7 @@ BGD_DECLARE(gdImagePtr) gdImageCreateFromXbm(FILE * fd)
 /* {{{ gdCtxPrintf */
 static void gdCtxPrintf(gdIOCtx * out, const char *format, ...)
 {
-	char buf[4096];
+	char buf[1024];
 	int len;
 	va_list args;
 
@@ -191,6 +191,9 @@ static void gdCtxPrintf(gdIOCtx * out, const char *format, ...)
 }
 /* }}} */
 
+/* The compiler will optimize strlen(constant) to a constant number. */
+#define gdCtxPuts(out, s) out->putBuf(out, s, strlen(s))
+
 /* {{{ gdImageXbmCtx */
 BGD_DECLARE(void) gdImageXbmCtx(gdImagePtr image, char* file_name, int fg, gdIOCtx * out)
 {
@@ -215,9 +218,26 @@ BGD_DECLARE(void) gdImageXbmCtx(gdImagePtr image, char* file_name, int fg, gdIOC
 		}
 	}
 
-	gdCtxPrintf(out, "#define %s_width %d\n", name, gdImageSX(image));
-	gdCtxPrintf(out, "#define %s_height %d\n", name, gdImageSY(image));
-	gdCtxPrintf(out, "static unsigned char %s_bits[] = {\n  ", name);
+	/* Since "name" comes from the user, run it through a direct puts.
+	 * Trying to printf it into a local buffer means we'd need a large
+	 * or dynamic buffer to hold it all. */
+
+	/* #define <name>_width 1234 */
+	gdCtxPuts(out, "#define ");
+	gdCtxPuts(out, name);
+	gdCtxPuts(out, "_width ");
+	gdCtxPrintf(out, "%d\n", gdImageSX(image));
+
+	/* #define <name>_height 1234 */
+	gdCtxPuts(out, "#define ");
+	gdCtxPuts(out, name);
+	gdCtxPuts(out, "_height ");
+	gdCtxPrintf(out, "%d\n", gdImageSY(image));
+
+	/* static unsigned char <name>_bits[] = {\n */
+	gdCtxPuts(out, "static unsigned char ");
+	gdCtxPuts(out, name);
+	gdCtxPuts(out, "_bits[] = {\n  ");
 
 	free(name);
 
@@ -234,9 +254,9 @@ BGD_DECLARE(void) gdImageXbmCtx(gdImagePtr image, char* file_name, int fg, gdIOC
 			if ((b == 128) || (x == sx && y == sy)) {
 				b = 1;
 				if (p) {
-					gdCtxPrintf(out, ", ");
+					gdCtxPuts(out, ", ");
 					if (!(p%12)) {
-						gdCtxPrintf(out, "\n  ");
+						gdCtxPuts(out, "\n  ");
 						p = 12;
 					}
 				}
@@ -248,6 +268,6 @@ BGD_DECLARE(void) gdImageXbmCtx(gdImagePtr image, char* file_name, int fg, gdIOC
 			}
 		}
 	}
-	gdCtxPrintf(out, "};\n");
+	gdCtxPuts(out, "};\n");
 }
 /* }}} */

programming_language: C