CVE-2026-23270
Published: 18 March 2026
Summary
CVE-2026-23270 is a high-severity Use After Free (CWE-416) vulnerability in Linux Linux Kernel. Its CVSS base score is 7.8 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 4.9th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SI-2 (Flaw Remediation) and CM-6 (Configuration Settings).
Deeper analysis
CVE-2026-23270 is a use-after-free (UaF) vulnerability in the Linux kernel's net/sched subsystem. The issue arises because, following a prior commit, the classify action can return TC_ACT_CONSUMED while the current socket buffer (skb) is held by the defragmentation engine, leading to a UaF when the engine later accesses the packet. The act_ct (connection tracking) action was not intended for use in the egress path, though some users have attached it there, exacerbating the problem in qdiscs that do not properly handle TC_ACT_CONSUMED.
A local attacker with low privileges can exploit this vulnerability due to its CVSS v3.1 base score of 7.8 (AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H). By attaching act_ct to inappropriate qdiscs, such as non-clsact/egress paths, the attacker can trigger the UaF condition during packet defragmentation, potentially achieving high-impact confidentiality, integrity, and availability effects, such as kernel crashes or arbitrary code execution.
The provided kernel stable patch references detail the mitigation, which restricts act_ct binding to only clsact/ingress qdiscs and shared blocks. This change maintains compatibility for clsact-based egress attachments while preventing the UaF in other configurations. Security practitioners should apply the relevant stable kernel updates, such as commits 11cb63b0d1a0, 380ad8b7c65e, 524ce8b4ea8f, 5a110ddcc99b, and 9deda0fcda5c, to affected systems.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-12913
Vulnerability details
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…
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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/
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Local UaF in kernel net/sched enables privilege escalation to kernel code execution.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Directly addresses the CVE by requiring timely remediation through application of kernel patches that restrict act_ct binding to clsact/ingress qdiscs and shared blocks, eliminating the UaF vulnerability.
Implements memory protection mechanisms that mitigate exploitation of the use-after-free in the net/sched defragmentation engine by preventing unauthorized memory access.
Enforces secure baseline configuration settings for the kernel's net/sched subsystem to prohibit attachment of act_ct actions to inappropriate qdiscs, reducing the risk of triggering the UaF.