CVE-2018-0949

Internet Explorer has a security “guardrail” meant to stop certain risky actions. In CVE-2018-0949, that guardrail can be sidestepped when the browser tries to access network locations (UNC paths) in a specific way. If someone tricks a user into opening a crafted link, the protection may not work as intended.

This matters if your business still runs Microsoft Internet Explorer 9, 10, or 11 on Windows. It’s only relevant when a crafted UNC-related request can be triggered—so the risk depends on whether users can be induced to open the right kind of link (user interaction is involved).

This is a security feature bypass in Internet Explorer affecting IE 9/10/11, and it’s categorized as medium severity. There’s no indication it’s being actively exploited in the wild (not listed in CISA KEV, and no public exploit code on record), so it’s not an immediate “fire now” situation—but you should patch promptly.

Confirm exposure

• Identify where Microsoft Internet Explorer is still in use across your business devices.
• Specifically check for Internet Explorer 9, 10, or 11.
• Also confirm which Windows versions those browsers are installed on, because Microsoft’s fix is delivered via Windows security updates.

Get the fix

• Use the Microsoft advisory for CVE-2018-0949 to determine the exact update(s) that apply to your environment:
  • https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2018-0949
• Install the recommended update(s) for your affected systems and restart if required.

Temporary workaround (if patching is delayed)

• Reduce the chance of triggering the issue by:
  • Training users not to open unexpected/untrusted links.
  • Avoiding links that reference network paths (UNC) from untrusted sources.
  • Disabling or limiting Internet Explorer usage if your business policy allows.

What to monitor after updating

• Verify the security update is installed via your standard patch-management reporting.
• Watch for internal reports of user clicks on suspicious links, especially links related to network paths (UNC), and ensure your email/browser filtering is functioning as intended.

Due date guidance

• Not listed in CISA KEV, so no CISA-mandated deadline applies based on the provided findings.

CVE-2018-0949 is described as an “Internet Explorer Security Feature Bypass Vulnerability” involving improper handling of requests to UNC (network) resources. The provided severity is medium, with conditions reflecting user interaction involvement (the scenario requires a user to trigger/open something rather than being purely background/network reachable).

Findings indicate:

• Not listed in CISA KEV (no confirmed CISA-tracked exploitation signal provided).
• No public exploit code on record.
• Patch information is available via the Microsoft advisory link.

Because exploitation is not confirmed by KEV in the findings, treat this as a patch-now item (medium impact and plausible attack paths) rather than an immediate incident response item.