Echo: linux: security update to 6.1.174-1

high Tenable Cloud Security Plugin ID 462330

Description

There are packages installed that are affected by a vulnerability referenced in the following CVE:

- 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.
(CVE-2026-43503)

Solution

Update the linux library and its related packages to version 6.1.174-1 or later.

Plugin Details

Severity: High

ID: 462330

Version: Revision 1.1

Type: Local

Family: Echo Local Security Checks

Published: 10/2/2026

Updated: 10/2/2026

Risk Information

VPR

Risk Factor: Critical

Score: 9.2

Percentile: 99.76

CVSS v2

Risk Factor: Medium

Base Score: 6.8

Temporal Score: 5.6

Vector: CVSS2#AV:L/AC:L/Au:S/C:C/I:C/A:C

CVSS Score Source: CVE-2026-43503

CVSS v3

Risk Factor: High

Base Score: 7

Temporal Score: 6.5

Vector: CVSS:3.0/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

Temporal Vector: CVSS:3.0/E:F/RL:O/RC:C

Vulnerability Information

Exploit Available: true

Exploit Ease: Exploits are available

Patch Publication Date: 5/24/2026

Vulnerability Publication Date: 5/15/2026

Exploitable With

Core Impact

Metasploit (Sample Linux Priv Esc, DescriptionThis exploit module illustrates how a vulnerability could be exploitedin an linux command for priv esc.})

Reference Information

CVE: CVE-2026-43503

Detections

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