VulnerabilityPublished 4 Dec 2025Updated 31 Jul 2026

CVE-2025-40236: Linux kernel · virtio-net: zero unused hash fields

Affects Linux kernelSource GCVE Database

Not known to be exploited · fixed in 6.17.0-1007.7~24.04.1 : update Linux kernel when convenient.

Data as of 26 Oct 2026, 13:47 UTC

Severity

Medium

Rated by Threat Radar · No CVSS score from NVD or the CNA

EPSS: 0.1% chance of exploitation in 30 days – higher than 8% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 6.17.0-1007.7~24.04.1, 6.17.0-1008.8~24.04.1, 6.17.0-1008.8 +6

Exploitation evidence

Disclosed: evidence found.
CVE published 4 Dec 2025
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.

What to do

Upgrade to a fixed release listed under Affected software.

Patches and advisories

Affected software

Product	Affected	Fixed in
Ubuntu 25.10linux`pkg:deb/ubuntu/linux?arch=source&distro=questing`Other threats	Affected <6.17.0-14.14	Fixed in 6.17.0-14.14
Ubuntu 25.10linux-aws`pkg:deb/ubuntu/linux-aws?arch=source&distro=questing`Other threats	Affected <6.17.0-1007.7	Fixed in 6.17.0-1007.7
Ubuntu 25.10linux-azure`pkg:deb/ubuntu/linux-azure?arch=source&distro=questing`Other threats	Affected <6.17.0-1008.8	Fixed in 6.17.0-1008.8
Ubuntu 25.10linux-azure-fde`pkg:deb/ubuntu/linux-azure-fde?arch=source&distro=questing`Other threats	Affected 6.17.0-1003.3 – 6.17.0-1017.17 10 affected builds	Fixed in–
Ubuntu 25.10linux-gcp`pkg:deb/ubuntu/linux-gcp?arch=source&distro=questing`Other threats	Affected <6.17.0-1007.7	Fixed in 6.17.0-1007.7
Ubuntu 25.10linux-oracle`pkg:deb/ubuntu/linux-oracle?arch=source&distro=questing`Other threats	Affected <6.17.0-1007.7	Fixed in 6.17.0-1007.7

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A patch is available and should be applied by updating to the fixed Linux kernel versions as specified by the Ubuntu security advisories USN-8029-1 and USN-8030-1. After updating, a system reboot is required to activate the patched kernel. Due to an ABI change, all third-party kernel modules must be recompiled and reinstalled. Users should follow standard system update procedures to ensure the fix is applied properly.

Description

A vulnerability in the Linux kernel's virtio-net driver was fixed that involved failure to zero unused hash fields when Generic Segmentation Offload (GSO) tunnel is negotiated. This flaw could lead to information leakage between different sides. The issue has been addressed by zeroing the unused hash fields. The vulnerability affects multiple Linux kernel versions, including various Ubuntu kernel releases. A patch is available and users are advised to update and reboot their systems. Due to an ABI change, recompilation and reinstallation of third-party kernel modules may be required after updating.

Impact

The vulnerability may allow information leakage through uninitialized memory fields in the virtio-net driver when GSO tunnels are negotiated. This could potentially expose sensitive kernel memory contents to an attacker with access to the affected network interfaces. However, there is no indication of active exploitation in the wild. The impact is limited to information disclosure rather than code execution or privilege escalation.

Summary

The Linux kernel's virtio-net driver contained a vulnerability (CVE-2025-40236) where the function virtio_net_hdr_tnl_from_skb() failed to zero unused rxhash fields when a GSO tunnel was negotiated. This omission could result in leaking kernel memory information across different network contexts. The issue was resolved by ensuring these unused hash fields are zeroed properly. The vulnerability affects a wide range of Linux kernel versions, particularly those used in Ubuntu's linux-hwe-edge and linux-gcp packages. The vendor advisory from Ubuntu confirms the availability of patches in kernel versions 6.17.0-14.14 and related updates. Users must update their kernel packages and reboot to apply the fix. The update also requires recompilation of third-party kernel modules due to ABI changes.

References

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