Linux: Write-what-where Condition

What to do

1. Update Linux to a6cb440f274a22456ef3e86b457344f1678f38f9 or ab8b995323e5237041472d07e5055f5f7dcdf15b or fe785bb3a8096dffcc4048a85cd0c83337eeecad or 5d55c7336f8032d434adcc5fab987ccc93a44aec, whichever matches your release line, or a later version.
2. Update SIMATIC S7-1500 CPU 1518-4 PN/DP MFP to V3.1.7 or a later version.
3. Update SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP to V3.1.7 or a later version.

Affected products and versions

Version data comes from the organisation that assigned the CVE; 8 further products are omitted here. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector

LocalThe attacker needs local access or must trick a user into running something.

Attack complexity

LowNo special conditions are needed; the attack works reliably.

Privileges required

LowA basic user account is enough.

User interaction

NoneNo action by a victim is required.

Scope

ChangedThe attack can reach beyond the vulnerable component into other systems.

Confidentiality

HighAll data handled by the component can be read.

Integrity

HighData or code can be modified at will.

Availability

HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H. Scored by CNA.

Official description

In the Linux kernel, the following vulnerability has been resolved: xfrm: esp: avoid in-place decrypt on shared skb frags MSG_SPLICE_PAGES can attach pages from a pipe directly to an skb. TCP marks such skbs with SKBFL_SHARED_FRAG after skb_splice_from_iter(), so later paths that may modify packet data can first make a private copy. The IPv4/IPv6 datagram append paths did not set this flag when splicing pages into UDP skbs. That leaves an ESP-in-UDP packet made from shared pipe pages looking like an ordinary uncloned nonlinear skb. ESP input then takes the no-COW fast path for uncloned skbs without a frag_list and decrypts in place over data that is not owned privately by the skb. Mark IPv4/IPv6 datagram splice frags with SKBFL_SHARED_FRAG, matching TCP. Also make ESP input fall back to skb_cow_data() when the flag is present, so ESP does not decrypt externally backed frags in place. Private nonlinear skb frags still use the existing fast path. This intentionally does not change ESP output. In esp_output_head(), the path that appends the ESP trailer to existing skb tailroom without calling skb_cow_data() is not reachable for nonlinear skbs: skb_tailroom() returns zero when skb->data_len is nonzero, while ESP tailen is positive. Thus ESP output will either use the separate destination-frag path or fall back to skb_cow_data().

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Write-what-where Condition

Timeline

1. May 8, 2026CVE record published.
2. May 8, 2026CISA published its SSVC assessment (exploitation: poc, automatable: no, technical impact: total).
3. November 11, 2026Record last changed materially (score, affected products, status or references).

References

Recent Write-what-where Condition vulnerabilities

• 7.8 High severity

  Acronis DeviceLock DLP: Write-what-where Condition

  CVE-2026-41952Apr 29, 2026Acronis
• 9.8 Critical severity

  Bareiron: Write-what-where Condition

  CVE-2025-69809Mar 16, 2026P2r3
• 8.8 High severity

  Red Hat Enterprise Linux 10: Write-what-where Condition

  CVE-2025-9900Sep 23, 2025Red HatEPSS 1%
• 8.8 High severity

  ImageMagick: Write-what-where Condition

  CVE-2025-55298Aug 26, 2025ImageMagickEPSS 4.68%
• 7.8 High severity

  Substance3D - Stager: Write-what-where Condition

  CVE-2024-45142Oct 9, 2024Adobe
• 8.2 High severity

  intel_300: Write-what-where Condition

  CVE-2024-36877Aug 12, 2024MSI

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