System admins are being advised to pay careful attention to one of Microsoft's Patch Tuesday updates that could allow an attack from the company side of a firewall to gains control of PCs without user intervention.
MS13-001, which affects Windows 7 and Windows 2008 Server R2, was flagged was one of two remote code execution vulnerabilities marked 'critical' in Microsoft's advance notification bulletin this weekend.
The flaw is in the Windows Print Spooler; according to security vendor nCircle, an attacker could target large numbers of systems inside a network at their default privilege level by sending a job via the spooler. Such an attack would work without user interaction.
Although that made an external attack impossible - an attacker on the public side of a firewall would have no way of reaching the targets - getting an attack inside a company would be possible either via an unpatched laptop or an infected USB stick, nCircle pointed out.
Large enterprises would patch this issue as part of the test cycle but smaller organisations might remain vulnerable for longer, the company warned.
A temporary fix would be to turn off the print spooler by editing the registry.
The second critical in the new update, MS13-002, is in Windows Core XML Services, last updated in July 2012 with MS12-043.
Microsoft has not fully patched the recent zero day hole in IE 6,7 and 8 (CVE-2012-4792) for which there are circulating watering hole attacks, despite a fix on 2 January which it later emerged could be bypassed.