CVE-2021-21703

NameCVE-2021-21703
DescriptionIn PHP versions 7.3.x up to and including 7.3.31, 7.4.x below 7.4.25 and 8.0.x below 8.0.12, when running PHP FPM SAPI with main FPM daemon process running as root and child worker processes running as lower-privileged users, it is possible for the child processes to access memory shared with the main process and write to it, modifying it in a way that would cause the root process to conduct invalid memory reads and writes, which can be used to escalate privileges from local unprivileged user to the root user.
SourceCVE (at NVD; CERT, LWN, oss-sec, fulldisc, bugtraq, EDB, Metasploit, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, Mageia, GitHub advisories/code/issues, web search, more)
ReferencesDLA-2794-1, DSA-4992-1, DSA-4993-1
Debian Bugs997003

Vulnerable and fixed packages

The table below lists information on source packages.

Source PackageReleaseVersionStatus
php7.3 (PTS)buster, buster (security)7.3.31-1~deb10u1fixed
php7.4 (PTS)bullseye (security), bullseye7.4.30-1+deb11u1fixed

The information below is based on the following data on fixed versions.

PackageTypeReleaseFixed VersionUrgencyOriginDebian Bugs
php7.0sourcestretch7.0.33-0+deb9u12DLA-2794-1
php7.0source(unstable)(unfixed)
php7.3sourcebuster7.3.31-1~deb10u1DSA-4993-1
php7.3source(unstable)(unfixed)
php7.4sourcebullseye7.4.25-1+deb11u1DSA-4992-1
php7.4source(unstable)7.4.26-1997003
php8.0source(unstable)(unfixed)

Notes

Fixed in 8.0.12, 7.4.25
PHP Bug: http://bugs.php.net/81026
https://github.com/php/php-src/commit/fadb1f8c1d08ae62b4f0a16917040fde57a3b93b
https://www.ambionics.io/blog/php-fpm-local-root
https://www.openwall.com/lists/oss-security/2021/10/26/7

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