A php7.3 security update has been released for Debian GNU/Linux 10 to address an out-of-bounds read and write flaw was discovered in the PHP-FPM code.

DSA 4993-1: php7.3 security update

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Debian Security Advisory DSA-4993-1 security@debian.org
  https://www.debian.org/security/ Salvatore Bonaccorso
October 25, 2021   https://www.debian.org/security/faq
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Package : php7.3
CVE ID : CVE-2021-21703

An out-of-bounds read and write flaw was discovered in the PHP-FPM code,
which could result in escalation of privileges from local unprivileged
user to the root user.

For the oldstable distribution (buster), this problem has been fixed
in version 7.3.31-1~deb10u1.

We recommend that you upgrade your php7.3 packages.

For the detailed security status of php7.3 please refer to its security
tracker page at:
  https://security-tracker.debian.org/tracker/php7.3

Further information about Debian Security Advisories, how to apply
these updates to your system and frequently asked questions can be
found at:   https://www.debian.org/security/