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CVE-2026-23270 — net/sched: Only allow act_ct to bind to clsact/ingress qdiscs and shared blocks

Affected: Linux, Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP, Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP, Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP

In the Linux kernel, the following vulnerability has been resolved:

net/sched: Only allow act_ct to bind to clsact/ingress qdiscs and shared blocks

As Paolo said earlier [1]:

"Since the blamed commit below, classify can return TC_ACT_CONSUMED while the current skb being held by the defragmentation engine. As reported by GangMin Kim, if such packet is that may cause a UaF when the defrag engine later on tries to tuch again such packet."

act_ct was never meant to be used in the egress path, however some users are attaching it to egress today [2]. Attempting to reach a middle ground, we noticed that, while most qdiscs are not handling TC_ACT_CONSUMED, clsact/ingress qdiscs are. With that in mind, we address the issue by only allowing act_ct to bind to clsact/ingress qdiscs and shared blocks. That way it's still possible to attach act_ct to egress (albeit only with clsact).

[1] https://lore.kernel.org/netdev/674b8cbfc385c6f37fb29a1de08d8fe5c2b0fbee.1771321118.git.pabeni@redhat.com/ [2] https://lore.kernel.org/netdev/cc6bfb4a-4a2b-42d8-b9ce-7ef6644fb22b@ovn.org/

RHSA-2026:13565 — Red Hat Security Advisory: kernel security update

kernel: Linux kernel: Denial of Service in libceph OSD client due to unreset sparse-read state kernel: Linux kernel: Use-after-free in traffic control (act_ct) may lead to denial of service or privilege escalation kernel: nfsd: fix heap overflow in NFSv4.0 LOCK replay cache kernel: crypto: algif_aead - Revert to operating out-of-place kernel: crypto: algif_aead - Fix minimum RX size check for decryption

RHSA-2026:21209 — Red Hat Security Advisory: kernel security update

kernel: proc: fix UAF in proc_get_inode() kernel: proc: use the same treatment to check proc_lseek as ones for proc_read_iter et.al kernel: net/sched: Make cake_enqueue return NET_XMIT_CN when past buffer_limit kernel: nbd: defer config unlock in nbd_genl_connect kernel: scsi: qla2xxx: Fix improper freeing of purex item kernel: Linux kernel: Denial of service and memory corruption in RDMA umad kernel: Linux kernel: Use-after-free in traffic control (act_ct) may lead to denial of service or privilege escalation kernel: Linux kernel: Use-after-free in bonding driver leads to denial of service kernel: md/bitmap: fix GPF in write_page caused by resize race