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Researchers Release Patch for NSA-linked "EsteemAudit" Exploit

Security researchers at enSilo have released a patch to keep vulnerable systems protected from a recently released Windows exploit allegedly used by the National Security Agency (NSA)-linked Equation Group.

Dubbed EsteemAudit, this exploit targets a remote desktop protocol (RDP) bug and can be abused to move laterally within a compromised organization’s network, as well as to infect victims with ransomware or backdoors, or to exfiltrate sensitive information.

The exploit might not be as popular as the EternalBlue exploit, which fueled large infections such as WannaCry or Adylkuzz, but it could prove as devastating.

EsteemAudit was made public last month when the hacking group known as the Shadow Brokers decided to release a new set of exploits and tools allegedly stolen from the NSA-linked Equation Group last year. Soon after, Microsoft said the vulnerabilities had been patched in March.

The hackers initially put the tools up for auction, but decided to release some of them for free after failing to attract buyers. Last week, the Shadow Brokers announced plans to launch a subscription service and share more exploits to members for a monthly fee.

Unlike EternalBlue, which affects a variety of Windows versions, EsteemAudit only works on Windows XP and Windows Server 2003, which supposedly limits its overall impact. However, this also means that an official patch is unlikely to arrive from Microsoft, as it no longer offers support for these platform iterations.

Because of that, enSilo decided to release a persistent patch for these systems and keep users safe from attacks possibly leveraging the exploit. The decision was fueled by the fact that a large number of machines continue to use Windows XP and Server 2003, the researchers say.

“Upon login for each session, Windows will create a new instance of winlogon. The patch will be loaded into winlogon.exe (only if it is an RDP session) to perform in memory patching (hotpatching) of EsteemAudit. Any attempt to use EsteemAudit to infect the patched machine will inevitably fail,” enSilo explains.

Installing this patch, however, doesn’t render Windows XP or Server 2003 systems fully secure, as hundreds of other vulnerabilities impacting them still exist and will never be patched. This patch resolves only the vulnerability exploited by EsteemAudit and works on both x86 and x64 platform versions.

The patch is available for download on enSilo’s website and is installed by an installation program after accepting the terms of usage. Uninstallation is supported by signaling an event (which will remove the patch in memory) and unregistering the patch from loading into subsequent RDP sessions.

“The patch for Windows XP and Server 2003 supports silent installation and does not require a reboot, which helps users avoid the required downtime typically associated with patch installations. Upon patching, any attempt to use an EsteemAudit exploit to infect a patched machine will inevitably fail,” the researchers say.

Related: EternalRocks Network Worm Leverages 7 NSA Hacking Tools

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