DescriptionA vulnerability was found in curl. The issue can occur when curl's HSTS check is bypassed to trick it to keep using HTTP. Using its HSTS support, curl can be instructed to use HTTPS instead of an insecure clear-text HTTP step even when providing HTTP in the URL. Suppose the hostname in the given URL first uses IDN characters that get replaced with ASCII counterparts as part of the IDN conversion. In that case, it can bypass the HSTS mechanism using the character UTF-8 U+3002 (IDEOGRAPHIC FULL STOP) instead of the common ASCII full stop (U+002E). Then in a subsequent request, it does not detect the HSTS state and makes a clear text transfer. Because it would store the information, IDN encoded but looked for it as IDN decoded.A vulnerability was found in curl. The issue can occur when curl's HSTS check is bypassed to trick it to keep using HTTP. Using its HSTS support, curl can be instructed to use HTTPS instead of an insecure clear-text HTTP step even when providing HTTP in the URL. Suppose the hostname in the given URL first uses IDN characters that get replaced with ASCII counterparts as part of the IDN conversion. In that case, it can bypass the HSTS mechanism using the character UTF-8 U+3002 (IDEOGRAPHIC FULL STOP) instead of the common ASCII full stop (U+002E). Then in a subsequent request, it does not detect the HSTS state and makes a clear text transfer. Because it would store the information, IDN encoded but looked for it as IDN decoded.