Created perl-DBI tracking bugs for this issue:

Affects: fedora-all [bug 1877423]

I marked this as a Low since it could be considered part of the software lifecycle or hardening, and the "fix" merely labels some functions as deprecated with comments. However, it may be worthwhile to note in the code.

The only place where the deprecation is mentioned is a comment in a header file.

-int      dbd_db_login6 _((SV *dbh, imp_dbh_t *imp_dbh, char *dbname, char *uid, char *pwd, SV*attribs));
+int      dbd_db_login6 _((SV *dbh, imp_dbh_t *imp_dbh, char *dbname, char *uid, char *pwd, SV*attribs)); /* deprecated */

It's not either a function attribute (so that a compiler could emit a warning), nor noticed in a DBI::DBD documentation. E.g. The closest text regarding dbd_db_login6() reads:

    Since DBI post v1.607, if a "dbd_db_login6_sv()" macro is defined (for a
    function like dbd_db_login6 but with scalar pointers for the dbname,
    username and password), it will be used instead. This will allow your
    login6 function to see if there are any Unicode characters in the
    dbname.

Also I'd like to note that those functions are not provided by DBI. DBI only provides their declarations in dbd_xsh.h to help the DBD drivers to implement them. So technically there is no vulnerability in DBI. It's in the driver that decides to implement the old interface that does not allow the driver to process Unicode characters properly. DBI common layer always prefer the safe functions:

void
_login(dbh, dbname, username, password, attribs=Nullsv)
    SV *        dbh
    SV *        dbname
    SV *        username
    SV *        password
    SV *        attribs
    CODE:
    {
    D_imp_dbh(dbh);
#if !defined(dbd_db_login6_sv)
    STRLEN lna;
    char *u = (SvOK(username)) ? SvPV(username,lna) : (char*)"";
    char *p = (SvOK(password)) ? SvPV(password,lna) : (char*)"";
#endif
#ifdef dbd_db_login6_sv
    ST(0) = dbd_db_login6_sv(dbh, imp_dbh, dbname, username, password, attribs) ? &PL_sv_yes : &PL_sv_no;
#elif defined(dbd_db_login6)
    ST(0) = dbd_db_login6(dbh, imp_dbh, SvPV_nolen(dbname), u, p, attribs) ? &PL_sv_yes : &PL_sv_no;
#else
    PERL_UNUSED_ARG(attribs);
    ST(0) = dbd_db_login( dbh, imp_dbh, SvPV_nolen(dbname), u, p) ? &PL_sv_yes : &PL_sv_no;
#endif
    }