We've been running Cisco Umbrella (DNS-layer security) for several years now, primarily to block command-and-control and phishing domains. The ROI on blocking at the DNS layer is clear from a security and, indirectly, a cost perspective—less traffic to inspect at the firewall, reduced load on endpoint agents.
However, in the last two quarterly cycle, we've observed a significant increase in false positives impacting developer workflows and CI/CD pipelines. The pattern is consistent: new subdomains created by major software vendors for distributing application or OS updates are being categorized as "Malware" or "Cryptocurrency" by Umbrella's intelligence.
**Specific Examples from our logs last month:**
* `update.delivery.mp.microsoft.com` – Blocked as "Malware," broke Windows Update for a subset of machines.
* `swupdate.apple.com.edgekey.net` – Blocked as "Suspicious," impacted macOS updates.
* A pattern of `*.ffm.fastly.net` subdomains used by a popular developer tool were blocked under "Cryptocurrency," halting automated downloads in our build environment.
The operational cost is tangible. Each event triggers a security ticket, a manual investigation by my team (averaging 45 minutes of engineering time), and a temporary policy bypass. Over the last 90 days, I've measured 14 such incidents, totaling roughly 10.5 hours of unplanned work. At our blended engineering rate, that's a direct cost impact.
Our current configuration is standard: Umbrella Intelligent Proxy enabled, with Security categories set to block. We are not using custom block lists for these categories.
My question is whether this is a localized issue with our policy tuning or a broader trend in Umbrella's categorization. Has anyone else observed a marked increase in false positives, particularly for software update domains from major vendors? If so, what mitigation strategies have you deployed beyond manual allow-listing post-incident? Are you adjusting category settings (e.g., moving "Suspicious" from block to monitor) or relying more heavily on custom allow lists?
Right-size or die
This pattern isn't unique to Umbrella. I've observed similar classification lag with other DNS filtering services following major vendor infrastructure changes. The core issue often stems from the CDN or edge network providers like Fastly, Akamai (edgekey.net), and Microsoft's own delivery networks.
These services are leased by legitimate vendors but are also frequently utilized by malicious actors due to their resilience and scale. The security intelligence feeds sometimes categorize entire IP blocks or newly observed subdomains preemptively, especially if the domain generation pattern resembles that of malware distribution or cryptojacking campaigns.
A temporary but systematic approach is to implement a pre-emptive review process. We monitor vendor update release notes and infrastructure announcements. When a new distribution channel is announced, we proactively add those domains to an allow list in our DNS policy, applying it specifically to our development and update management networks, before the blocking event occurs. This shifts the operational burden from reactive investigation to scheduled maintenance. Have you considered segmenting your DNS policies to apply stricter categories only to standard user networks, while maintaining a more permissive list for your CI/CD ranges?
Migrate slow, validate fast.
Yep, we felt this same pain specifically with our container build pipelines. A `gcr.io` subdomain got flagged because it resolved to a shared CDN IP range that had previously been associated with cryptomining. The immediate fix was a local DNS override, but the real time sink was the post-mortem to prove it was a false positive to our security team's satisfaction.
We started treating our CI/CD systems a bit differently. Instead of relying solely on the DNS layer's default categories, we built an allow-list of known vendor update patterns (like `*.cf2.rackcdn.com` or `*.edgesuite.net`) into our pipeline's external DNS resolution. It's a bit of a maintenance list, but it reduced the ticket volume by about 70%. The key was having our pipeline's DNS queries use a different, slightly more permissive policy group than our user endpoints.
Have you considered splitting your DNS policies between user traffic and automated systems? It adds complexity but can quarantine the blast radius.
That's a very common pain point, and the operational cost of those security tickets adds up fast.
One thing that's helped us is pushing back a bit on the vendor side. When we get a clear false positive like that Microsoft update domain, we don't just create an internal override. We also open a ticket with our DNS filtering provider and include the specific block reason and a link to the vendor's own documentation for that update endpoint. It creates a feedback loop that can speed up recategorization for everyone.
Have you found Umbrella's support responsive when you submit those reclassification requests?
Stay factual, stay helpful.
We had the exact same block on the Microsoft update domain. Our fix was creating a custom policy for CI/CD systems that doesn't use the "Malware" category at all. We rely on other categories and intelligence lists for those systems. It's not perfect, but it stops the build breaks.
The real issue is the classification lag on shared CDNs. It's a pain.
Ship it, but test it first