CVE-2026-43503

Published May 23, 2026

Last updated a month ago

Container Security

Overview

AI description

Automated description summarized from trusted sources.

CVE-2026-43503, dubbed "DirtyClone," is a vulnerability found within the Linux kernel's networking subsystem, specifically affecting the `net/skbuff` component. The core of the issue lies in certain "frag-transfer helpers," such as `__pskb_copy_fclone()` and `skb_shift()`, which fail to correctly propagate the `SKBFL_SHARED_FRAG` bit in `skb_shinfo()->flags` when network packet fragments (skbs) are moved between source and destination. This flag is crucial as it indicates whether the packet fragments reference shared page-cache memory. This propagation failure results in a state where the destination `skb` maintains references to shared, page-cache-backed pages but incorrectly reports that it lacks shared fragments. This discrepancy can be exploited by in-place writers, such as the ESP (Encapsulating Security Payload) input processing, which relies on the `skb_has_shared_frag()` function to determine if shared pages require copying before modification. An unprivileged user could leverage this flaw, for instance, by using an `nft 'dup to <local>'` rule or other `nf_dup_ipv4()` / `xt_TEE` callers, to write into the page cache of a root-owned read-only file.

Description: 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.
Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
NVD status: Modified
Products: linux_kernel

Risk scores

CVSS 3.1

Type: Secondary
Base score: 8.8
Impact score: 6
Exploitability score: 2
Vector string: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Severity: HIGH

Weaknesses

nvd@nist.gov: NVD-CWE-noinfo
0b0ca135-0b70-47e7-9f44-1890c2a1c46c: CWE-664

Hype score: Not currently trending

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References

Sources include official advisories and independent security research.