GoKawiil8 min read
On April 29, 2026, a Linux kernel local privilege escalation vulnerability was publicly disclosed under the name "Copy Fail" ( CVE-2026-31431 ). Cloudflare’s Security and Engineering teams began assessing the vulnerability as soon as it was disclosed. We reviewed the exploit technique, evaluated exposure across our infrastructure, and validated that our existing behavioral detections could identify the exploit pattern within minutes.
There was no impact to the Cloudflare environment, no customer data was at risk, and no services were disrupted at any point. Read on to learn how our preparedness paid off.
Background
Our Linux kernel release process
Cloudflare operates a global Linux server infrastructure at an immense scale, with datacenters located across 330 cities . We maintain a custom Linux kernel build based on the community's Long-Term Support (LTS) versions to manage updates effectively at this volume. At any given time, we may utilize multiple LTS versions from various series, such as 6.12 or 6.18, which benefit from extended update periods.
The community regularly merges and releases security and stability updates which trigger an automated job to generate a new internal kernel build approximately every week. These builds undergo testing in our staging data centers to ensure stability before a global rollout. Following a successful release, the Edge Reboot Release (ERR) pipeline manages a systematic update and reboot of the edge infrastructure on a four-week cycle. Our control plane infrastructure typically adopts the most recent kernel, with reboots scheduled according to specific workload requirements.
By the time a CVE becomes public knowledge, the necessary fix has typically been integrated into stable Linux LTS releases for several weeks. Our established procedures ensure that we have already deployed these patches.
At the time of the "Copy Fail" disclosure, the majority of our infrastructure was running the 6.12 LTS version, while a subset of machines had begun transitioning to the newer 6.18 LTS release.
About the Copy Fail vulnerability
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