CVE-2025-39926

What it actually does

In the generic netlink subsystem, genl_bind() incorrectly invokes the registered bind() callback even after an authorization check returns -EPERM, allowing the operation to proceed despite the permission failure.

Why it matters to the business

Attackers could bypass intended access controls on Linux systems to perform unauthorized networking operations, increasing risk of privilege escalation or exposure of kernel-managed resources.

How an attack unfolds

An attacker sends a crafted generic netlink message targeting a family with a bind callback. The kernel evaluates permissions, returns -EPERM, yet still executes the bind handler, allowing the unauthorized action to complete.

How to fix it

Update the Linux kernel to the commit 98c9d884047a3051c203708914a874dece3cbe54 or an equivalent patched release that corrects the authorization check order in genl_bind().

How to confirm the fix worked

Confirm the fix commit is present in the kernel source tree and verify through testing that bind callbacks are skipped when permission checks return -EPERM.

Typical attack path

1. Locate a generic netlink family exposing a bind callback
2. Issue a bind request lacking required capabilities or permissions
3. Trigger genl_bind() to evaluate and reject with -EPERM
4. Observe the bind callback executing anyway and perform the restricted action

How to detect it

Review kernel audit logs and netlink trace events for bind requests that produce -EPERM followed by successful callback execution or subsequent privileged operations.

What your security team should do

• Apply the referenced kernel commit or newer stable release across all affected systems
• Audit custom generic netlink families for reliance on bind callbacks
• Increase monitoring of netlink traffic until patches are deployed