In the Linux kernel, the following vulnerability has been resolved:
net: skbuff: propagate shared-frag marker through frag-transfer helpers
Two frag-transfer helpers (__pskb_copy_fclone() and skb_shift()) fail
to propagate the SKBFL_SHARED_FRAG bit in skb_shinfo()->flags when
moving frags from source to destination. __pskb_copy_fclone() defers
the rest of the shinfo metadata to skb_copy_header() after copying
frag descriptors, but that helper only carries over gso_{size,segs,
type} and never touches skb_shinfo()->flags; skb_shift() moves frag
descriptors directly and leaves flags untouched. As a result, the
destination skb keeps a reference to the same externally-owned or
page-cache-backed pages while reporting skb_has_shared_frag() as
false.
The mismatch is harmful in any in-place writer that uses
skb_has_shared_frag() to decide whether shared pages must be detoured
through skb_cow_data(). ESP input is one such writer (esp4.c,
esp6.c), and a single nft 'dup to <local>' rule -- or any other
nf_dup_ipv4() / xt_TEE caller -- is enough to land a pskb_copy()'d
skb in esp_input() with the marker stripped, letting an unprivileged
user write into the page cache of a root-owned read-only file via
authencesn-ESN stray writes.
Set SKBFL_SHARED_FRAG on the destination whenever frag descriptors
were actually moved from the source. skb_copy() and skb_copy_expand()
share skb_copy_header() too but linearize all paged data into freshly
allocated head storage and emerge with nr_frags == 0, so
skb_has_shared_frag() returns false on its own; they need no change.
The same omission exists in skb_gro_receive() and skb_gro_receive_list().
The former moves the incoming skb's frag descriptors into the
accumulator's last sub-skb via two paths (a direct frag-move loop and
the head_frag + memcpy path); the latter chains the incoming skb whole
onto p's frag_list. Downstream skb_segment() reads only
skb_shinfo(p)->flags, and skb_segment_list() reuses each sub-skb's
shinfo as the nskb -- both p and lp must carry the marker.
The same omission also exists in tcp_clone_payload(), which builds an
MTU probe skb by moving frag descriptors from skbs on sk_write_queue
into a freshly allocated nskb. The helper falls into the same family
and warrants the same fix for consistency; no TCP TX-side in-place
writer is currently known to reach a user page through this gap, but
a future consumer depending on the marker would regress silently.
The same omission exists in skb_segment(): the per-iteration flag
merge takes only head_skb's flag, and the inner switch that rebinds
frag_skb to list_skb on head_skb-frags exhaustion does not fold the
new frag_skb's flag into nskb. Fold frag_skb's flag at both sites
so segments drawing frags from frag_list members carry the marker.
References
Configurations
Configuration 1 (hide)
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History
23 Jul 2026, 11:10
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| Summary |
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02 Jul 2026, 12:17
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| References |
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30 Jun 2026, 03:19
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| CWE | CWE-664 | |
| References |
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26 Jun 2026, 18:57
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| CWE | NVD-CWE-noinfo | |
| First Time |
Linux linux Kernel
Linux |
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| References | () https://git.kernel.org/stable/c/12401fcfb01f53ccc63ab0a3246570fe8f3105ee - Patch | |
| References | () https://git.kernel.org/stable/c/179f1852bdedc300e373e807cc102cd81feff196 - Patch | |
| References | () https://git.kernel.org/stable/c/48f6a5356a33dd78e7144ae1faef95ffc990aae0 - Patch | |
| References | () https://git.kernel.org/stable/c/989214c66884d70716d83dc1d0bf5e16287bf349 - Patch | |
| References | () https://git.kernel.org/stable/c/9bc9d6d6967a2239aa57af2aa53554eddd640d20 - Patch | |
| References | () https://git.kernel.org/stable/c/fbeab9555564a1b98e8582cd106dfe46c4606991 - Patch | |
| References | () https://git.kernel.org/stable/c/fc6eb39c55e97df2f94ad974b8a5bbcd019da2c8 - Patch | |
| References | () https://git.kernel.org/stable/c/ff375cc75f9167168db38e0464a482d5fbc8d81d - Patch | |
| CPE | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:7.1:rc2:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:7.1:rc3:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:7.1:rc1:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:7.1:rc4:*:*:*:*:*:* |
30 May 2026, 11:17
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| CVSS |
v2 : v3 : |
v2 : unknown
v3 : 8.8 |
25 May 2026, 07:16
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| References |
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23 May 2026, 14:16
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| New CVE |
Information
Published : 2026-05-23 12:17
Updated : 2026-07-23 11:10
NVD link : CVE-2026-43503
Mitre link : CVE-2026-43503
CVE.ORG link : CVE-2026-43503
JSON object : View
Products Affected
linux
- linux_kernel
CWE