Two things I'd personally suggest.

One, do a non-greedy match with .*? (although I'd wonder if there's no data -- perhaps use .+? instead). Not critical, just precautionary.

And two, verify your match (this could probably be more elegant, but just to illustrate the point):

my $msg;
if (/msg=(.*?) Src/) {
    $msg = $1;
}
#else {
# possible error message here, whatever is appropriate
#}
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