Bug 2516854 (CVE-2026-74290)

Summary: CVE-2026-74290 kernel: net/sched: cls_flow: Dont expose folded kernel pointers
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's `cls_flow` module. A local user, by operating a traffic control (tc) classifier within a user or network namespace, could manipulate specific parameters. This manipulation allows the user to recover sensitive 32-bit folded kernel pointer values, leading to information disclosure.
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Description OSIDB Bzimport 2026-08-15 06:36:58 UTC 
In the Linux kernel, the following vulnerability has been resolved:

net/sched: cls_flow: Dont expose folded kernel pointers

The flow classifier falls back to addr_fold() for fields that are missing
from packet headers. In map mode, userspace controls mask, xor, rshift,
addend and divisor, and can observe the resulting classid through class
statistics. This allows a tc classifier in a user/network namespace to
recover the 32-bit folded value of skb->sk, skb_dst() or skb_nfct().

Align with standard kernel practices for pointer hashing and replace the
XOR folding with a keyed siphash (which is cryptographically secure)
Comment 1 Keith Grant 2026-08-20 14:51:48 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026081547-CVE-2026-74290-9a3d@gregkh/T