CVE-2026-72338
Received Received - Intake

Heap OOB Write in Linux Kernel's tc offload

Publication date: 2026-08-15

Last updated on: 2026-08-15

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: net/sched: act_pedit: fix TOCTOU heap OOB write in tc offload There is a TOCTOU race condition in flower lockless approach between sizing a flow_rule buffer and filling it. zdi-disclosures@trendmicro.com reports: The cls_flower classifier operates with TCF_PROTO_OPS_DOIT_UNLOCKED (fl_change runs without RTNL), while RTM_NEWACTION holds RTNL, so the independent locking domains make the race reachable in practice. KASAN confirms: BUG: KASAN: slab-out-of-bounds in tcf_pedit_offload_act_setup+0x81b/0x930 Write of size 4 at addr ffff888001f27520 by task poc-toctou/312 The buggy address is located 0 bytes to the right of allocated 288-byte region [ffff888001f27400, ffff888001f27520) (cache kmalloc-512) Note: The result is a heap OOB write attacker-controlled content into the adjacent slab object (requires CAP_NET_ADMIN). The fix introduces reading tcfp_nkeys under act->tcfa_lock in all places using a new tcf_pedit_nkeys_locked() which replaces the old tcf_pedit_nkeys(). Additionally we close the remaining TOCTOU window between the sizing read and the fill reads by more careful accounting. Rather than silently truncating the key count, which leads to incorrect action semantics offloaded to hardware and secondary OOB writes if the remaining capacity is zero or consumed by prior actions, we enforce remaining capacity checks and return -ENOSPC if the required space exceeds the remaining capacity.

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Meta Information

Published
2026-08-15
Last Modified
2026-08-15
Generated
2026-08-15
AI Q&A
2026-08-15
EPSS Evaluated
N/A
NVD
CVE-2026-72338
EUVD
EUVD-2026-59237

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *

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Exploitability

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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This is a TOCTOU (Time-of-Check to Time-of-Use) race condition in the Linux kernel's net/sched act_pedit module. It occurs when the cls_flower classifier and RTM_NEWACTION operate with different locking domains, allowing an attacker to trigger a heap out-of-bounds write. The flaw enables writing attacker-controlled data into adjacent slab memory, requiring CAP_NET_ADMIN privileges.

Detection Guidance

This vulnerability is specific to the Linux kernel's net/sched subsystem and requires CAP_NET_ADMIN privileges to exploit. Detection involves checking kernel logs for KASAN slab-out-of-bounds errors related to tcf_pedit_offload_act_setup. Monitor for crashes or memory corruption in network-related processes.

Impact Analysis

If exploited, this vulnerability could allow local attackers with CAP_NET_ADMIN privileges to corrupt kernel memory, potentially leading to system crashes, privilege escalation, or unauthorized code execution. The impact depends on the kernel's memory layout and adjacent slab objects.

Mitigation Strategies

Apply the latest kernel patches that fix this issue. Restrict CAP_NET_ADMIN capabilities to untrusted users. Monitor network traffic for unusual patterns. If using hardware offloading, disable it temporarily until patched.

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