A critical use-after-free bug within the **Linux** kernel's **SCTP** (Stream Control Transmission Protocol) networking code has been identified, allowing for full root privileges on affected hosts. Researchers at **Tencent Zhuque Lab** have demonstrated how this vulnerability, active since 2008, can be leveraged to escape containers and gain control over the underlying machine. Tracked as **CVE-2026-64564** and named **SCTPhantom** by its discoverers, the flaw was publicly disclosed on August 6, shortly after the kernel CVE team assigned the identifier. As of this writing, no public exploit code has surfaced, and the vulnerability is not yet listed in **CISA's Known Exploited Vulnerabilities** catalog.  ### Impact and Reach The **SCTPhantom** vulnerability is local, not remote, and requires **SCTP** to be reachable on the target system, which somewhat limits its exposure. However, where these conditions are met, **Tencent Zhuque Lab** reported achieving root access on various kernel builds, including **Debian 13**, **Ubuntu 24.04**, **Rocky Linux 9**, **RHEL 9**, and **OpenCloudOS**. **SCTP** is a transport protocol that enables a single connection to operate over multiple network paths simultaneously. A key feature, dynamic address reconfiguration, allows peers to add or remove these addresses during an active connection. ### The Mechanics of the Flaw The bug stems from a logic error in how the kernel handles identity during address deletion. The kernel verifies a delete request against the packet's source address but then acts on a path selected using a different address embedded within the message. As per the **kernel's own advisory**, a specific sequence of messages—one carrying an address, a delete for that same address, followed by a wildcard delete—can free the path and then reuse the now-dangling pointer. This leaves the connection pointing to memory that the kernel has already released. ### Patch and Remediation The fix, which has already been shipped, prevents a delete operation from targeting the path currently being processed by the message. The vulnerability has been present in every **Linux** kernel release since version 2.6.25 in 2008. Stable kernels 7.1.6, 6.18.42, 6.12.101, and 6.6.148, released on August 3, incorporate the fix. Users running older kernels with **SCTP** enabled are strongly advised to update immediately. ### Container Escape Claims **Tencent's** claim of a container escape is based on their internal testing. In their **write-up**, the lab initially found that an early exploit version required `net.sctp.addip_enable` and `net.sctp.addip_noauth_enable` sysctls to be enabled, suggesting **CAP_NET_ADMIN** as a prerequisite. However, they later discovered an alternative method that bypasses these requirements by enabling the features per socket. The lab asserts that their escape test maintained the default seccomp profile and did not grant **CAP_NET_ADMIN** or **CAP_SYS_ADMIN**. They reported a success rate of six out of eight attempts in achieving root on the host. It's important to note that, as of now, no external party has independently reproduced these container escape claims. The **Tencent** write-up does not specify the container runtime used in their tests. The lab itself acknowledges that factors like socket access, seccomp profiles, and user-namespace policies can influence exposure. An **openKylin advisory** on the same bug only reports kernel panic and denial of service. ### Unsettled Severity and Broader Context The severity score for **CVE-2026-64564** remains somewhat unsettled. **Tencent** assigned it an 8.5 under **CVSS v4.0**, while the **NVD** had not yet assigned a score or weakness classification by August 7. Organizations should be aware that vendors often backport fixes without updating to a new upstream version. Therefore, relying solely on a kernel version string might not accurately indicate whether a system is patched; checking distribution-specific trackers is recommended. A separate dangling-transport use-after-free bug in the same **SCTP** code was patched on August 6, meaning the August 3 stable releases do not include its fix. For systems where **SCTP** is not required, blocking the module entirely removes the attack surface. **Tencent** credits the discovery to **Corvus AI**, a multi-agent research pipeline developed for kernel analysis. **SCTPhantom** is the latest in a series of long-dormant kernel flaws, including **GhostLock** in July, brought to light with machine assistance this year. Its disclosure also coincides with **Zapscape**, an unrelated **KVM** escape vulnerability, with both fixes included in the same four stable kernel releases.