Bug 1878761 (CVE-2020-28935) - CVE-2020-28935 unbound: symbolic link traversal when writing PID file
Summary: CVE-2020-28935 unbound: symbolic link traversal when writing PID file
Alias: CVE-2020-28935
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
Target Milestone: ---
Assignee: Red Hat Product Security
QA Contact:
Depends On: 1968662 1968663 1968664 1878762 1899058 1910711
Blocks: 1878763
TreeView+ depends on / blocked
Reported: 2020-09-14 13:26 UTC by Pedro Sampaio
Modified: 2021-09-22 14:57 UTC (History)
5 users (show)

Fixed In Version: unbound 1.13.0
Doc Type: If docs needed, set a value
Doc Text:
A symbolic link traversal vulnerability was found in unbound in the way it writes its PID file while starting up. This flaw allows a local attacker with access to the unbound user to set up a link to another file, owned by root, and make unbound overwrite it during its next restart, destroying the original content. The highest threat from this vulnerability is integrity.
Clone Of:
Last Closed: 2021-05-18 20:36:12 UTC

Attachments (Terms of Use)

Description Pedro Sampaio 2020-09-14 13:26:02 UTC
A flaw was found in Unbound in the way it writes its PID file during startup. A local attacker with access to the unbound user could abuse this issue to create a symbolic link where unbound is going to write its PID file, so that a following start of unbound would follow the symlink and write the PID in another file chosen by the attacker. This operation could overflow files owned by root on the system.

Upstream issue:

Comment 1 Pedro Sampaio 2020-09-14 13:26:28 UTC
Created unbound tracking bugs for this issue:

Affects: fedora-all [bug 1878762]

Comment 3 Riccardo Schirone 2020-10-19 14:26:34 UTC

If SELinux is enabled in Enforcing mode (the default value in Red Hat Enterprise Linux 8), this kind of attack is prevented as unbound would be blocked from accessing the symbolic link file.

Comment 6 Riccardo Schirone 2020-11-19 14:12:21 UTC

Name: Mason Loring Bliss (Red Hat)

Comment 13 errata-xmlrpc 2021-05-18 15:37:36 UTC
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8

Via RHSA-2021:1853 https://access.redhat.com/errata/RHSA-2021:1853

Comment 14 Product Security DevOps Team 2021-05-18 20:36:12 UTC
This bug is now closed. Further updates for individual products will be reflected on the CVE page(s):


Note You need to log in before you can comment on or make changes to this bug.