CVE-2026-23003: Linux kernel · ip6_tunnel: use skb_vlan_inet_prepare() in __ip6_tnl_rcv()
Affects Linux kernelSource GCVE Database
Not known to be exploited · CVSS 7.5 High · fixed in 5.15.0-1105.112~20.04.1 : patch Linux kernel soon.
Data as of 26 Oct 2026, 11:07 UTC
- EPSS
- 0.5% chance of exploitation in 30 days – higher than 45% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available – fixed in 5.15.0-1105.112~20.04.1, 5.15.0-1110.119~20.04.1, 5.15.0-1106.115~20.04.1 +59
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:HExploitation evidence
Disclosed: evidence found.
CVE published 25 Jan 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.
What to do
Upgrade to a fixed release listed under Affected software.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Ubuntu 25.10linuxpkg:deb/ubuntu/linux@6.17.0-40.40?arch=source&distro=questingOther threats | Affected
| Fixed in– |
Ubuntu 25.10linux-awspkg:deb/ubuntu/linux-aws@6.17.0-1019.19?arch=source&distro=questingOther threats | Affected
| Fixed in– |
Ubuntu 25.10linux-azurepkg:deb/ubuntu/linux-azure@6.17.0-1020.20?arch=source&distro=questingOther threats | Affected
| Fixed in– |
Ubuntu 25.10linux-azure-fdepkg:deb/ubuntu/linux-azure-fde@6.17.0-1017.17?arch=source&distro=questingOther threats | Affected
| Fixed in– |
Ubuntu 25.10linux-gcppkg:deb/ubuntu/linux-gcp@6.17.0-1020.22?arch=source&distro=questingOther threats | Affected
| Fixed in– |
Ubuntu 25.10linux-oraclepkg:deb/ubuntu/linux-oracle@6.17.0-1018.18?arch=source&distro=questingOther threats | Affected
| Fixed in– |
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 Azure kernel versions as provided by the vendor. The vendor advisory from Ubuntu confirms that the issue is resolved in updated packages. After updating, a system reboot is required. Due to an ABI change, recompilation and reinstallation of third-party kernel modules may be necessary. Users should follow the vendor's update instructions to remediate this vulnerability.
Description
A vulnerability in the Linux kernel's IPv6 tunnel handling was resolved by using skb_vlan_inet_prepare() in the __ip6_tnl_rcv() function to properly handle VLAN encapsulations. The issue was identified by syzbot and involved uninitialized values in ECN decapsulation code. This flaw could lead to a denial of service (system crash) due to kernel memory corruption. The vulnerability affects multiple Linux Azure kernel versions prior to specific patched releases. A fix is available and included in updated kernel packages.
References
- ubuntu.com/security/CVE-2026-23003 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2026-23003 (opens in a new tab)
- git.kernel.org/linus/81c734dae203757fb3c9eee6f9896386940776bd (opens in a new tab)
- git.kernel.org/stable/c/81c734dae203757fb3c9eee6f9896386940776bd (opens in a new tab)
- git.kernel.org/stable/c/b9f915340f25cae1562f18e1eb52deafca328414 (opens in a new tab)
- git.kernel.org/stable/c/df5ffde9669314500809bc498ae73d6d3d9519ac (opens in a new tab)
- ubuntu.com/security/notices/USN-8162-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8180-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8180-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-8186-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8187-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8188-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8180-3 (opens in a new tab)
- ubuntu.com/security/notices/USN-8180-4 (opens in a new tab)
- ubuntu.com/security/notices/USN-8180-5 (opens in a new tab)
- ubuntu.com/security/notices/USN-8243-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8180-6 (opens in a new tab)
- ubuntu.com/security/notices/USN-8275-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8278-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8289-1 (opens in a new tab)