Kernel network-stack bug in widely deployed Linux; remote-triggerable memory corruption can disrupt infrastructure and escalate to root/RCE.
CVE-2026-72139
Linux kernel TCP MD5/AO use-after-free enabling remote kernel memory corruption.
Is CVE-2026-72139 being exploited?
Not confirmed. CVE-2026-72139 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.58% probability of exploitation in the next 30 days.
How severe is CVE-2026-72139?
CVE-2026-72139 is rated Critical with a CVSS score of 9.8. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-72139?
Yes. A fix has been recorded for CVE-2026-72139. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-72139 affect?
CVE-2026-72139 affects Linux kernel (net/ipv4 tcp MD5/AO handling). Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-72139?
Apply vendor Linux kernel updates immediately and reboot network-facing hosts.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote memory-corruption via TCP MD5/AO race during connect; can cause kernel crashes, DoS, or escalate to root/remote code execution.
Immediate action required
- affected>= 51e547e8c89c661f6fbede4a28b1d33b13625683 and < 33a1bee413628378fd036a4f2b17ba86b0bc560c
- affected>= 51e547e8c89c661f6fbede4a28b1d33b13625683 and < da48b9bf1eb95a9cfd09d615ca58cfc2b03de369
- affected>= 51e547e8c89c661f6fbede4a28b1d33b13625683 and < b74cd55038905d5e74c1de109ab78a30b2ea0e1f
- affected6.18
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.