CVE-2026-23247: Linux kernel · tcp: secure_seq: add back ports to TS offset
Affects Linux kernelSource GCVE Database
Not known to be exploited · CVSS 5.5 Medium.
Data as of 26 Oct 2026, 17:16 UTC
- EPSS
- 0.1% chance of exploitation in 30 days – higher than 5% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:HExploitation evidence
Disclosed: evidence found.
CVE published 18 Mar 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
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Ubuntu 25.10linuxpkg:deb/ubuntu/linux?arch=source&distro=questingOther threats | Affected
| Fixed in– |
Ubuntu 25.10linux-awspkg:deb/ubuntu/linux-aws?arch=source&distro=questingOther threats | Affected
| Fixed in– |
Ubuntu 25.10linux-azurepkg:deb/ubuntu/linux-azure?arch=source&distro=questingOther threats | Affected
| Fixed in– |
Ubuntu 25.10linux-azure-fdepkg:deb/ubuntu/linux-azure-fde?arch=source&distro=questingOther threats | Affected
| Fixed in– |
Ubuntu 25.10linux-gcppkg:deb/ubuntu/linux-gcp?arch=source&distro=questingOther threats | Affected
| Fixed in– |
Ubuntu 25.10linux-oraclepkg:deb/ubuntu/linux-oracle?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 fix has been implemented in the Linux kernel by reverting the previous change and reintroducing TCP ports into the timestamp offset randomization. Users should apply the updated kernel versions that include this fix. Since this is a kernel-level patch, upgrading to the fixed versions listed is the recommended remediation.
Description
A vulnerability in the Linux kernel's TCP implementation related to timestamp offset randomization was resolved by reverting a previous change and reintroducing TCP ports into the timestamp offset calculation. This addresses an off-path TCP source port leakage via a SYN cookie side-channel reported by Zhouyan Deng. The fix includes a single siphash() computation to generate both an Initial Sequence Number (ISN) and a timestamp offset.
References
- ubuntu.com/security/CVE-2026-23247 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2026-23247 (opens in a new tab)
- git.kernel.org/linus/165573e41f2f66ef98940cf65f838b2cb575d9d1 (opens in a new tab)
- git.kernel.org/stable/c/165573e41f2f66ef98940cf65f838b2cb575d9d1 (opens in a new tab)
- git.kernel.org/stable/c/46e5b0d7cf55821527adea471ffe52a5afbd9caf (opens in a new tab)
- git.kernel.org/stable/c/eae2f14ab2efccdb7480fae7d42c4b0116ef8805 (opens in a new tab)