CVERadar
HIGH · CVSS 3.1 8.8Metasploit modulePublic PoCEPSS 1.99% (p80)Threat level 55

CVE-2026-43503: CVE-2026-43503: In the Linux kernel, the following vulnerability has been resolved: net: skbuff: propagat…

linux · linux kernel · NVD published 2026-05-23 · posted 2026-05-21 · last modified 2026-10-17

What it is

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.

WeaknessCWE-691CWE-664
CVSS vectorCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H (source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67)
ATT&CK tacticsn/a

Exploitation evidence

First exploit evidence seen: 2026-05-21 (earliest date across the sources below).

Exploited in the wild

No source on this site lists in-the-wild exploitation yet (CISA KEV, VulnCheck KEV).

Public exploit code

Metasploit

GitHub proof-of-concept repositories

8 public repositories from 8 accounts, first seen 2026-06-25. Most starred: 0xBlackash/CVE-2026-43503 (37 stars), view repository.

Verify before running: public PoCs can be malicious. Read the code and only run it in an isolated lab. A PoC means exploit code is public, not that this CVE is exploited in the wild.

Sources: Rapid7 Metasploit Framework module metadata · nomi-sec/PoC-in-GitHub.

No ATT&CK techniques could be mapped or inferred for this CVE yet.

How to fix it

Fixed versions

  • linux linux kernel: upgrade to 5.10.257 or later (affected from 3.9)
  • linux linux kernel: upgrade to 5.15.208 or later (affected from 5.11)
  • linux linux kernel: upgrade to 6.1.174 or later (affected from 5.16)
  • linux linux kernel: upgrade to 6.6.141 or later (affected from 6.2)
  • linux linux kernel: upgrade to 6.12.91 or later (affected from 6.7)
  • linux linux kernel: upgrade to 6.18.33 or later (affected from 6.13)
  • linux linux kernel: upgrade to 7.0.10 or later (affected from 6.19)

Derived from the NVD CPE configuration (versionEndExcluding / versionEndIncluding). Always confirm with the vendor advisory.

Vendor advisories and patches

Detection Generic guidance

    Response checklist Generic guidance

    1. Inventory: find every instance of the affected product and version (include internet-facing and forgotten ones).
    2. Patch or mitigate per the vendor advisory; if you cannot patch, remove internet exposure or apply the vendor workaround.
    3. Assume compromise if the system was exposed before patching: hunt for the indicators in the advisory and review logs back to the disclosure date.
    4. Rotate credentials and secrets stored on or used by the affected system if compromise cannot be ruled out.

    Sources