CVE Catalog

CVE-2026-23270

HighCVSS 7.8
Published: Updated: Translated: NVD NIST

Exploitation Probability (EPSS)

Low risk
0.12%

2th percentile - higher than 2% of all known CVEs

Summary

A vulnerability was found in the Linux kernel's act_ct (Connection Tracking) module for the network scheduler (net/sched). The issue arises from allowing act_ct in the egress path, which can lead to a Use-After-Free (UaF) due to improper handling of the TC_ACT_CONSUMED state by most qdiscs. The patch restricts act_ct binding to clsact/ingress qdiscs and shared blocks only.

Risk Assessment

The risk for the organization includes potential remote code execution or system crash (kernel panic) by sending specially crafted network traffic triggering a UaF in the kernel. Systems with Connection Tracking enabled on egress interfaces are affected.

Recommendation

Immediately update the Linux kernel to a version containing the fix (commit net/sched: Only allow act_ct to bind to clsact/ingress qdiscs). Until patched, avoid using act_ct in the egress path or restrict it to clsact.

Other vulnerabilities in Linux kernel

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Original NVD description (English source)

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/[email protected]/

Vulnerability data from NVD (NIST) · CISA KEV · EPSS