The bug traces to Linux 2.6.25 in 2008 and has been present in every kernel released since, researchers say — an 18‑year‑old use‑after‑free in SCTP networking code that has been tracked as CVE‑2026‑64564 and dubbed "SCTPhantom."
CVE-2026-64564 (SCTPhantom): what the flaw is and how it works
The vulnerability is a local use‑after‑free in the Linux implementation of SCTP (Stream Control Transmission Protocol) and its dynamic address reconfiguration feature. According to the kernel advisory summarized by the reporting lab, a single SCTP message can carry an address, a delete for that address, and then a wildcard delete. The kernel checks the delete request against the packet's source address but acts on a path it selected using a different address inside the same message, freeing the path and then reusing a now‑dead pointer so the connection can point at memory the kernel has already released.
The bug is not remote‑exploitable in the abstract: it is local and requires SCTP to be reachable on the target, conditions that the reporting group says limit exposure. Per the reporting, a patch changes the code to refuse a delete aimed at the path the message is being processed against.
Tencent Zhuque Lab, Corvus AI, and the container‑escape claim
Tencent's Zhuque Lab disclosed SCTPhantom on August 6 and credits the original find to Corvus AI, a multi‑agent research pipeline it uses for kernel work. The lab reports it used the bug to obtain full root on tested kernel builds and to escape a container to reach the underlying host.
In early exploit development the lab says an exploit path required the sysctls net.sctp.addip_enable and net.sctp.addip_noauth_enable to be switched on, which made CAP_NET_ADMIN appear to be a prerequisite. The lab later found a route that enabled the same features per socket so it could leave those sysctls untouched. For its container escape experiments the lab reports keeping the default seccomp profile and granting neither CAP_NET_ADMIN nor CAP_SYS_ADMIN; by its count, six of eight attempts reached root on the host.
No public exploit code had surfaced at the time of writing, and The Hacker News found no entry for the flaw in CISA's Known Exploited Vulnerabilities catalog as of August 7. The lab's write‑up does not name the container runtime it tested against, and no independent reproductions were reported as of August 7.
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See what we buildKernel fixes, releases, and related patches
The fix has already shipped in the stable kernel series: 7.1.6, 6.18.42, 6.12.101 and 6.6.148, all released August 3, which close the described use‑after‑free. A second "dangling‑transport" use‑after‑free in the same code was patched on August 6; that fix came after the August 3 stable releases, so those stable kernels do not carry the August 6 patch. Vendors commonly backport fixes into downstream kernels, the reporting notes, so a kernel version string alone will not determine whether a given machine is fixed — administrators must check their distribution's tracker.
Where SCTP is not required, the reporting recommends blocking the module to remove the attack surface entirely.
Observed and scored severity
Tencent assigned a CVSS v4.0 score of 8.5 to SCTPhantom. At the time of reporting NVD had assigned neither a score nor a weakness classification, and public exploit code had not been observed. The reporting reiterates that the flaw is local and requires SCTP reachability, which are constraining factors in assessing real‑world exposure.
What this means for container operators, distribution maintainers, and security teams
- Container operators: review seccomp profiles, granted capabilities, and any socket access patterns; Tencent's lab reached root without CAP_NET_ADMIN or CAP_SYS_ADMIN in several tests, and the lab notes that socket access and user‑namespace policy can shift exposure.
- Distribution maintainers: confirm whether your distribution has backported the August 3 fixes (and the subsequent August 6 fix where applicable) rather than relying on an upstream kernel version string; publish clear tracker entries so operators can verify coverage.
- Security teams and administrators: if SCTP is unused, consider blocking the SCTP kernel module to remove the attack surface; otherwise, prioritize kernel updates that include the stable 7.1.6, 6.18.42, 6.12.101 or 6.6.148 releases or equivalent backports.
SCTPhantom joins a string of long‑dormant kernel issues surfaced this year with machine assistance, the lab says — the report names GhostLock in July as a prior example — and it arrives the same day as Zapscape, an unrelated KVM escape; the four August 3 stable releases carry fixes for both issues. The practical question left by the record so far is whether independent researchers will reproduce Tencent's container‑escape results and whether vendors' backports will be promptly visible in distribution trackers. For now, the immediate, verifiable steps are straightforward: check your distribution tracker and update kernels or block SCTP where it is not needed.
