Pulse Secure Desktop Client (Windows) 5.3 Elevation of Privilege Vulnerability | The Missing Link

Discovered by Matt Bush on behalf of The Missing Link Security

Vulnerability Details

Versions of Pulse Secure Desktop Client 5.3 up to and including R6.0 build 1769 on Windows contain an elevation of privilege vulnerability due to insecure file and directory ACLs.

The default installation of the product grants BUILTIN\Users members effective Modify permissions to the "C:\ProgramData\Pulse Secure\Logging" folder.

The PulseSecureService service runs as BUILTIN\System by default. When this service starts it attempts to open the file "debuglog.log" in the unsecured directory. If this file is not present (ie, the service is running for the first time, or if the file has been deleted), the service creates the file. The service grants members of the BUILTIN\Everyone group (F) permissions on this file.

When the service is not running, an attacker running in the context of an unprivileged user may abuse the weak permissions in order to create a directory junction and object manager symbolic link to cause an arbitrary file to be written to an arbitrary location when the service is started. The unprivileged attacker can then overwrite the contents of the created file with arbitrary content.

This vulnerability can be exploited to achieve elevation of privilege by leveraging it for DLL preloading in the PulseSecureService process, or to carry out DLL search order hijacking in other privileged processes.

Affected Versions

Pulse Secure Desktop Client 5.3 (All versions)

Remediation: Upgrade to Pulse Secure Desktop Client 9.0Rx.

CVSS 3.0 Base Score: 7.9




13/05/2018: Vendor notified and advised of 60 day disclosure deadline

17/05/2018: Vendor acknowledges report

26/07/2018: Vendor requests more time to test fixes

13/09/2018: Vendor is offered an additional 30 days to apply fixes

24/10/2018: Public disclosure

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