CVE-2026-74739
Received Received - Intake

Heap-based Out-of-Bounds Read in Linux Kernel cls_u32

Publication date: 2026-08-26

Last updated on: 2026-08-26

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: net/sched: cls_u32: skip hash tables in u32_bind_class() u32_walk() enumerates both struct tc_u_hnode and struct tc_u_knode through the walker callback. u32_bind_class() unconditionally casts the passed fh to tc_u_knode and accesses &n->res, so when fh is actually a tc_u_hnode, which has no tcf_result member, this results in a slab-out-of-bounds read of res->classid in tc_cls_bind_class(). The issue can be reproduced with the following commands: tc qdisc add dev lo root handle 1: hfsc tc class add dev lo parent 1: classid 1:1 hfsc sc rate 1000kbit tc filter add dev lo parent 1:1 protocol ip prio 1 u32 match u32 0 0 flowid 1:1 tc class add dev lo parent 1: classid 1:2 hfsc sc rate 2000kbit Fix this by skipping hash tables via the TC_U32_KEY(handle) check.

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Meta Information

Published
2026-08-26
Last Modified
2026-08-26
Generated
2026-08-26
AI Q&A
2026-08-26
EPSS Evaluated
N/A
NVD
CVE-2026-74739
EUVD
EUVD-2026-66569

Affected Vendors & Products

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

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This vulnerability in the Linux kernel involves a slab-out-of-bounds read in the net/sched cls_u32 module. The issue occurs when u32_bind_class() incorrectly processes a tc_u_hnode structure as a tc_u_knode, leading to an invalid memory access in tc_cls_bind_class().

Detection Guidance

The vulnerability can be detected by checking for the presence of vulnerable kernel versions and attempting to reproduce the issue using the provided commands. Run the commands to see if they trigger the slab-out-of-bounds read. Example: tc qdisc add dev lo root handle 1: hfsc; tc class add dev lo parent 1: classid 1:1 hfsc sc rate 1000kbit; tc filter add dev lo parent 1:1 protocol ip prio 1 u32 match u32 0 0 flowid 1:1; tc class add dev lo parent 1: classid 1:2 hfsc sc rate 2000kbit.

Impact Analysis

This vulnerability could allow an attacker to read sensitive kernel memory, potentially leading to information disclosure or system crashes. It may be exploited via network traffic manipulation if unprivileged users can configure traffic control rules.

Mitigation Strategies

Apply the kernel patch that introduces the fix by skipping hash tables via the TC_U32_KEY(handle) check. Update your Linux kernel to a version that includes this patch. Monitor vendor advisories for updates.

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