medium
6.7
CWE
59
Advisory Published
CVE Published
Updated

CVE-2021-35939

First published: Mon May 24 2021(Updated: )

In response to <a href="https://access.redhat.com/security/cve/CVE-2017-7500">CVE-2017-7500</a> and <a href="https://access.redhat.com/security/cve/CVE-2017-7501">CVE-2017-7501</a>, it was decided that the policy of RPM is "Only follow directory symlinks owned by target directory owner or root." [1]. This check was only implemented for the parent directory of the file to be created. If an untrusted user owns another ancestor directory, the problem remains unfixed. An actual exploit requires that a similar directory structure exists both at the location where RPM operates and for the files the attacker wants to get control over. Packages with such paths do exist in the real world, however. For example, in openSUSE both matomo and icinga2 ship a 'Pdo/Mysql.php' somewhere in the file system, with different ownership. A compromised 'matomo' user can create a symlink /srv/www/matomo/core/Tracker/Db -&gt; /usr/share/icingaweb2/library/vendor/Zend/Db/Adapter/ and on the next update of matomo, RPM would replace the 'Pdo/Mysql.php' of icinga2 and give ownership of it to the 'matomo' user. A fix for this requires a messy ball of code using O_PATH to manually walk the whole directory structure and manually resolving symlinks, like in [1] and [2]. References: 1: <a href="https://github.com/systemd/systemd/blob/a5648b809457d120500b2acb18b31e2168a4817a/src/basic/fs-util.c#L716">https://github.com/systemd/systemd/blob/a5648b809457d120500b2acb18b31e2168a4817a/src/basic/fs-util.c#L716</a> 2: <a href="https://build.suse.de/package/view_file/SUSE:Maintenance:13179/permissions.SUSE_SLE-15-SP1_Update/0007-chkstat-fix-privesc-CVE-2019-3690.patch?expand=1">https://build.suse.de/package/view_file/SUSE:Maintenance:13179/permissions.SUSE_SLE-15-SP1_Update/0007-chkstat-fix-privesc-CVE-2019-3690.patch?expand=1</a> 3. <a href="https://bugzilla.suse.com/show_bug.cgi?id=1157883">https://bugzilla.suse.com/show_bug.cgi?id=1157883</a>

Credit: secalert@redhat.com

Affected SoftwareAffected VersionHow to fix
Rpm Rpm<4.18
Redhat Enterprise Linux=8.0
redhat/rpm<4.18.0
4.18.0

Remedy

https://github.com/rpm-software-management/rpm/commit/96ec957e281220f8e137a2d5eb23b83a6377d556

Remedy

https://github.com/rpm-software-management/rpm/pull/1919

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Reference Links

Frequently Asked Questions

  • What is CVE-2021-35939?

    CVE-2021-35939 is a vulnerability that allows a local unprivileged user to potentially gain root privileges on certain Linux systems.

  • Which software is affected by CVE-2021-35939?

    The affected software includes RPM version up to 4.18.0 on Red Hat Enterprise Linux 8.0.

  • What is the severity of CVE-2021-35939?

    CVE-2021-35939 has a severity rating of medium with a CVSS score of 6.7.

  • How can an attacker exploit CVE-2021-35939?

    An attacker with local unprivileged access who owns an ancestor directory can exploit this vulnerability to gain root privileges.

  • Is there a fix available for CVE-2021-35939?

    Yes, a fix is available for CVE-2021-35939. It is recommended to update to RPM version 4.18.0 or later.

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