E2B Sandboxes Aren't Affected by Copy Fail (CVE-2026-31431). Here's why.

CVE-2026-31431 is a critical vulnerability disclosed by Theori, affecting most Linux systems since 2017, allowing deterministic root access when running untrusted code due to a flaw in the algif_aead kernel module combined with the splice() function. This vulnerability enables a 4-byte overwrite in the kernel's page cache, which can be exploited to gain root access, posing a significant threat in shared-kernel environments like Kubernetes clusters and cloud SaaS platforms. However, E2B sandboxes remain unaffected due to their architecture, which uses separate Firecracker microVMs for each sandbox, ensuring isolated kernels and memory. The vulnerability's potential impact is mitigated by patching affected systems or disabling the algif_aead module, and it's recommended to block AF_ALG socket creation on container platforms to enhance security.