Bug 2568683 (CVE-2026-99284)

Summary:	CVE-2026-99284 kernel: kernel: privilege escalation via missing shared fragment flag in skb_zerocopy
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	high	Docs Contact:
Priority:	high
Version:	unspecified	Keywords:	Security
Target Milestone:	---
Target Release:	---
Hardware:	All
OS:	Linux
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Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in the Linux kernel. A local unprivileged user could exploit this flaw to achieve privilege escalation by modifying read-only files cached in memory. The issue occurs because the networking subsystem fails to preserve shared memory indicators when transferring network data buffers. Consequently, subsequent operations such as Encapsulating Security Payload (ESP) decryption modify shared memory pages directly in place rather than creating a safe copy.	Story Points:	---
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Regression:	---	Mount Type:	---
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Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-11-07 20:51:14 UTC

In the Linux kernel, the following vulnerability has been resolved:

net: skbuff: propagate shared-frag marker in skb_zerocopy()

skb_zerocopy() moves frag descriptors from @from into @to and takes a
reference on each frag, but it does not copy skb_shinfo(from)->flags into
skb_shinfo(to)->flags.  A destination skb holding the same page-cache
backed frags as the source therefore reports skb_has_shared_frag() as
false.

That breaks the invariant relied on by later in-place writers.  ESP input
checks skb_has_shared_frag() before deciding whether an uncloned
nonlinear skb can skip skb_cow_data(); with the marker lost, an skb that
skb_zerocopy() built for nfnetlink_queue or for an openvswitch upcall is
decrypted in place, letting an unprivileged user write into the page
cache of a root-owned read-only file.

Propagate SKBFL_SHARED_FRAG when frag descriptors are copied, as done for
the other frag-transfer helpers.