CVE-2021-3655

What it actually does

Missing size validations on inbound SCTP packets allow the kernel to read uninitialized memory, resulting in limited information disclosure to a local user.

Why it matters to the business

On systems running vulnerable Linux kernels, a local user could access fragments of kernel memory, potentially exposing sensitive internal data and increasing the risk of further attacks on affected hosts.

How an attack unfolds

An attacker with local access crafts and sends specially formed SCTP packets that bypass size checks, causing the kernel to leak uninitialized memory contents back to user space.

How to fix it

Upgrade the Linux kernel to a version containing commit 7d2a07b769330c34b4deabeed939325c77a7ec2f or later; apply vendor-supplied updates for all affected distributions and reboot systems after installation.

How to confirm the fix worked

Verify the running kernel version against the fixed commit; review kernel configuration and source for the presence of updated SCTP packet size validation logic; test with crafted SCTP traffic in a lab environment to confirm no uninitialized memory is returned.

Typical attack path

1. Gain local user access on a target Linux system
2. Load or enable SCTP protocol handling if not already active
3. Transmit malformed inbound SCTP packets to trigger the validation flaw
4. Read the resulting uninitialized kernel memory contents

How to detect it

Review system logs for unusual SCTP packet handling errors or kernel warnings around packet processing; examine audit trails for unexpected local processes interacting with SCTP sockets; correlate with process execution history to identify potential local exploitation attempts.

What your security team should do

• Apply the kernel update containing commit 7d2a07b769330c34b4deabeed939325c77a7ec2f as soon as possible across all Linux deployments
• Restrict local user privileges where SCTP is enabled to reduce exposure
• Monitor for new kernel releases and schedule phased rollouts prioritizing internet-facing or high-value systems