This page says value is indeterminate, which is either unspecified or a trap, as you say: https://wiki.sei.cmu.edu/confluence/display/c/EXP33-C.+Do+no...
But.
This part says that reading an indeterminate value is, in fact, undefined behavior (line 11 in the table): https://wiki.sei.cmu.edu/confluence/display/c/CC.+Undefined+...
From 6.2.6.1¶5:
>Certain object representations need not represent a value of the object type. If the stored value of an object has such a representation and is read by an lvalue expression that does not have character type, the behavior is undefined. ... Such a representation is called a trap representation.
A read from uninitialized memory is not always UB.
Per http://www.open-std.org/jtc1/sc22/wg14/www/docs/dr_451.htm , the current standard is unclear in some respects, but the latest committee view is that that under the current standard any library function (including memcpy) may exhibit undefined behaviour when called with uninitialized memory, even when the uninitialized memory is of character type or is propagated through values of character type.