VulnerabilityPublished 19 Jul 2026Updated 20 Jul 2026

CVE-2026-63830: Linux kernel · net: skmsg: preserve sg.copy across SG transforms

Source GCVE Database

Authoritative record:CVE-2026-63830· Critical 9.4

Not known to be exploited · CVSS 9.4 Critical · fixed in f126eed589eec6f201405abbc398844042ef6d57 : patch Linux kernel as a priority.

Data as of 26 Oct 2026, 13:47 UTC

CVSS 3.1 base score

9.4Critical

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.4% chance of exploitation in 30 days – higher than 38% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in f126eed589eec6f201405abbc398844042ef6d57, d22cc92bc41290e5783a72375e0843d9435f6001, 406e8a651a7b854c41fecd5117bb282b3a6c2c6b +5

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: High
Availability: Low

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 19 Jul 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

ghsa-82mh-rf6q-rhp7

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ d3b18ad31f93d0b6bae105c679018a1ba7daa9ca, < f126eed589eec6f201405abbc398844042ef6d57	Fixed in f126eed589eec6f201405abbc398844042ef6d57
LinuxLinux	Affected ≥ d3b18ad31f93d0b6bae105c679018a1ba7daa9ca, < d22cc92bc41290e5783a72375e0843d9435f6001	Fixed in d22cc92bc41290e5783a72375e0843d9435f6001
LinuxLinux	Affected ≥ d3b18ad31f93d0b6bae105c679018a1ba7daa9ca, < 406e8a651a7b854c41fecd5117bb282b3a6c2c6b	Fixed in 406e8a651a7b854c41fecd5117bb282b3a6c2c6b
LinuxLinux	Affected ≥ d3b18ad31f93d0b6bae105c679018a1ba7daa9ca, < 31a110642b5fb5e61940cbcfb503445ac4f28017	Fixed in 31a110642b5fb5e61940cbcfb503445ac4f28017
LinuxLinux	Affected ≥ d3b18ad31f93d0b6bae105c679018a1ba7daa9ca, < 21ed9540a8e1906dfcbc1bb82ba9b4de4fa4bd6d	Fixed in 21ed9540a8e1906dfcbc1bb82ba9b4de4fa4bd6d
LinuxLinux	Affected ≥ d3b18ad31f93d0b6bae105c679018a1ba7daa9ca, < 9bb86d8184b37503816150c4a6ad3c17dfdbe827	Fixed in 9bb86d8184b37503816150c4a6ad3c17dfdbe827

AI-suggested

A fix for this vulnerability has been implemented in the Linux kernel to properly synchronize the sg.copy bitmap with scatterlist entries during all sk_msg transformations. Users should apply the official kernel updates that include this patch. Since this is a kernel-level fix, upgrading to a patched kernel version is the recommended remediation. Patch status is not explicitly stated here; check the vendor or Linux kernel advisories for the specific fixed kernel versions and apply updates accordingly.

Description

In the Linux kernel, the following vulnerability has been resolved: net: skmsg: preserve sg.copy across SG transforms The sk_msg sg.copy bitmap is part of the scatterlist entry ownership state. A set bit tells sk_msg_compute_data_pointers() not to expose the entry through writable BPF ctx->data. This protects entries backed by pages that are not private to the sk_msg, such as splice-backed file page-cache pages. Several sk_msg transform paths move, copy, split, or compact msg->sg.data[] entries without moving the matching sg.copy bit. This can make an externally backed entry arrive at a new slot with a clear copy bit. A later SK_MSG verdict can then expose sg_virt(sge) as writable ctx->data and BPF stores can modify the original page cache. Keep sg.copy synchronized with sg.data[] whenever entries are transferred, shifted, split, or copied into a new sk_msg. Clear the bit when an entry is replaced by a newly allocated private page or freed. This covers the BPF pull/push/pop helpers, sk_msg_shift_left/right(), sk_msg_xfer(), and tls_split_open_record(), including the partial tail entry created during TLS open-record splitting.

Impact

If exploited, this vulnerability could allow a BPF program to write to memory pages that are not private to the sk_msg, such as file page cache pages, potentially leading to unauthorized modification of kernel memory or cached file data. This could compromise system integrity or data confidentiality. However, no known exploits in the wild have been reported.

Summary

The vulnerability (CVE-2026-63830) in the Linux kernel's networking subsystem relates to the sk_msg scatterlist (sg) copy bitmap, which indicates ownership of scatterlist entries to prevent writable exposure of non-private pages to BPF contexts. Several sk_msg transform paths failed to move or update the sg.copy bit correctly when entries were moved, copied, split, or compacted. This desynchronization could lead to externally backed entries being exposed as writable through BPF, enabling modification of original page cache pages. The patch synchronizes the sg.copy bitmap with sg.data[] entries during all relevant sk_msg operations, including BPF helpers and TLS record splitting, preventing unauthorized writable exposure.

References

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