CVE-2018-8474

This is a problem in Lync for Mac 2011 where the app doesn’t handle certain “bad” messages safely. An attacker can send a malicious message over the network that causes the app’s protections to be skipped—like slipping past the guard at the door using a fake badge—potentially exposing information or allowing unwanted actions inside the app.

This matters if your business still runs Microsoft Lync (specifically “Lync for Mac 2011”) on Macs and those clients can receive messages over the network. The risk exists by default, meaning the vulnerability is present without extra special settings. It’s only a risk if an attacker can reach your Lync client and send specially crafted messages to it.

This is urgent enough to treat as a priority because attackers can bypass Lync’s security controls using crafted network messages without needing a login or user action. Public exploitation exists, and the overall likelihood signals are rising, so you should move quickly rather than waiting for a “quiet period.”

Confirm exposure

1. Identify all Mac machines where Microsoft Lync / “Lync for mac” (Lync for Mac 2011) is installed and actively used.
2. Confirm whether those clients receive Lync messages over the network in normal operations (especially from outside your trusted environment).

Apply the fix

1. Follow Microsoft’s remediation guidance for CVE-2018-8474 (the vendor advisory linked in your internal ticket/knowledge base, or provided by your IT vendor).
2. Upgrade or replace the affected Lync client with a fixed version as directed by Microsoft.

Temporary mitigation (if patching is delayed)

1. Reduce the ability for untrusted parties to send messages to your Lync clients (for example, tighten network paths and restrict inbound messaging sources to what you actually need).
2. Review any existing communications routing rules so only trusted peers/systems can reach Lync message delivery.
3. Make sure your users know not to click anything in suspicious message content—but note the key detail: the vulnerability does not require user interaction, so this is not a complete protection by itself.

What to monitor after changes

1. Monitor Lync client/network activity for unusual message patterns or abnormal spikes in message handling.
2. Ensure devices and the Lync client behavior match baseline after upgrading (to catch failed updates early).

KEV note

CVE-2018-8474 is not listed in the CISA KEV set (so prioritize based on vendor guidance and exploitation indicators rather than KEV alone).

Severity and nature

CVE-2018-8474 is a security feature bypass (CWE-20) affecting Microsoft Lync / Lync for Mac 2011. The client fails to properly sanitize specially crafted messages, allowing an attacker to bypass security controls.

Attack mechanics

• Attack vector: network-delivered messages.
• Authentication required: no.
• User interaction required: no.
• Reachability: the vulnerability is reachable by default.
  In practice, this means an attacker only needs the ability to send crafted messages to an affected Lync client over the network.

Exploitation status

• Public exploit(s): available (2 known).
• KEV: not listed.
• Exploit likelihood indicators: a rising likelihood prediction is present, though this should be treated as supportive (not as proof) since public exploit availability is already confirmed by the findings.

What KEV means here

Because it is not in KEV, it’s not specifically confirmed by CISA as a known exploited vulnerability in that dataset; however, the presence of public exploits and rising attention justify prioritizing remediation based on Microsoft’s guidance.