telnet: check sscanf() for correct number of matches

CVE-2021-22898

Bug: https://curl.se/docs/CVE-2021-22898.html

diff --git a/lib/telnet.c b/lib/telnet.c
index 26e0658ba9cc8ac2c62dec0dc9087375d5d09dea..fdd137fb0c047d67730d53af855d93e867ca8718 100644 (file)
--- a/lib/telnet.c
+++ b/lib/telnet.c
@@ -922,7 +922,7 @@ static void suboption(struct Curl_easy *data)
         size_t tmplen = (strlen(v->data) + 1);
         /* Add the variable only if it fits */
         if(len + tmplen < (int)sizeof(temp)-6) {
-          if(sscanf(v->data, "%127[^,],%127s", varname, varval)) {
+          if(sscanf(v->data, "%127[^,],%127s", varname, varval) == 2) {
             msnprintf((char *)&temp[len], sizeof(temp) - len,
                       "%c%s%c%s", CURL_NEW_ENV_VAR, varname,
                       CURL_NEW_ENV_VALUE, varval);