base64: Prevent undefined shift when parsing invalid base64 encoded data

Credit to OSS-Fuzz

1 files changed, 3 insertions, 3 deletions

diff --git a/src/base64.c b/src/base64.c
index ba8acca..ee02356 100644
--- a/src/base64.c
+++ b/src/base64.c
@@ -101,13 +101,13 @@ unsigned char *base64decode(const char *buf, size_t *size)
                         w3 = tmpval[2];
                         w4 = tmpval[3];
 
-                        if (w2 >= 0) {
+                        if (w1 >= 0 && w2 >= 0) {
                                 outbuf[p++] = (unsigned char)(((w1 << 2) + (w2 >> 4)) & 0xFF);
                         }
-                        if (w3 >= 0) {
+                        if (w2 >= 0 && w3 >= 0) {
                                 outbuf[p++] = (unsigned char)(((w2 << 4) + (w3 >> 2)) & 0xFF);
                         }
-                        if (w4 >= 0) {
+                        if (w3 >= 0 && w4 >= 0) {
                                 outbuf[p++] = (unsigned char)(((w3 << 6) + w4) & 0xFF);
                         }
                 }