Core:
    Fixed bug #80781 (Error handler that throws ErrorException infinite loop).
    Fixed bug #75776 (Flushing streams with compression filter is broken). (cmb) 04 Mar 2021, php 7.4.16
    Fixed #80706 (mail(): Headers after Bcc headers may be ignored).
Dba:
    Fixed bug #80817 (dba_popen() may cause segfault during RSHUTDOWN).
DOM:
    Fixed bug #66783 (UAF when appending DOMDocument to element).
FPM:
    Fixed bug #80024 (Duplication of info about inherited socket after pool removing).
FTP:
    Fixed bug #80880 (SSL_read on shutdown, ftp/proc_open).
Imap:
    Fixed bug #80710 (imap_mail_compose() header injection).
Intl:
    Fixed bug #80763 (msgfmt_format() does not accept DateTime references).
LibXML:
    Fixed bug #51903 (simplexml_load_file() doesn't use HTTP headers).
    Fixed bug #73533 (Invalid memory access in php_libxml_xmlCheckUTF8).
MySQLnd:
    Fixed bug #80713 (SegFault when disabling ATTR_EMULATE_PREPARES and MySQL 8.0).
    Fixed bug #80837 (Calling stmt_store_result after fetch doesn't throw an error).
    Fixed bug #78680 (mysqlnd's mysql_clear_password does not transmit null-terminated password).
Opcache:
    Fixed bug #80805 (create simple class and get error in opcache.so).
    Fixed bug #80950 (Variables become null in if statements).
Pcntl:
    Fixed bug #79812 (Potential integer overflow in pcntl_exec()).
PCRE:
    Fixed bug #80866 (preg_split ignores limit flag when pattern with \K has 0-width fullstring match).
PDO_ODBC:
    Fixed bug #80783 (PDO ODBC truncates BLOB records at every 256th byte).
PDO_pgsql:
    Fixed bug #80892 (PDO::PARAM_INT is treated the same as PDO::PARAM_STR).
phpdbg:
    Fixed bug #80757 (Exit code is 0 when could not open file).
Session:
    Fixed bug #80774 (session_name() problem with backslash).
    Fixed bug #80889 (Cannot set save handler when save_handler is invalid).
SOAP:
    Fixed bug #69668 (SOAP special XML characters in namespace URIs not encoded).
Standard:
    Fixed bug #78719 (http wrapper silently ignores long Location headers).
    Fixed bug #80771 (phpinfo(INFO_CREDITS) displays nothing in CLI).
    Fixed bug #80838 (HTTP wrapper waits for HTTP 1 response after HTTP 101).
    Fixed bug #80915 (Taking a reference to $_SERVER hides its values from phpinfo()).
    Fixed bug #80654 (file_get_contents() maxlen fails above (2**31)-1 bytes).
MySQLi:
    Fixed bug #74779 (x() and y() truncating floats to integers).
OPcache:
    Fixed bug #80682 (opcache doesn't honour pcre.jit option).
OpenSSL:
    Fixed bug #80747 (Providing RSA key size < 512 generates key that crash PHP).
Phar:
    Fixed bug #75850 (Unclear error message wrt. __halt_compiler() w/o semicolon) (cmb)
    Fixed bug #70091 (Phar does not mark UTF-8 filenames in ZIP archives).
    Fixed bug #53467 (Phar cannot compress large archives).
SPL:
    Fixed bug#80719 (Iterating after failed ArrayObject::setIteratorClass() causes Segmentation fault).
Zip:
    Fixed bug #80648 (Fix for bug 79296 should be based on runtime version).