What’s Vulnerable › Vulnerabilities

CVE-2025-39764: netfilter: ctnetlink: remove refcounting in expectation dumpers

• Severity: medium (CVSS 5.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-09-11 · updated 2026-10-19

Description

In the Linux kernel, the following vulnerability has been resolved: netfilter: ctnetlink: remove refcounting in expectation dumpers Same pattern as previous patch: do not keep the expectation object alive via refcount, only store a cookie value and then use that as the skip hint for dump resumption. AFAICS this has the same issue as the one resolved in the conntrack dumper, when we do if (!refcount_inc_not_zero(&exp->use)) to increment the refcount, there is a chance that exp == last, which causes a double-increment of the refcount and subsequent memory leak.

Affected products

• Linux kernel: from 2.6.23 before 6.16.2; 6.17-rc1 — fixed in 6.16.2

How to fix

Upgrade to a fixed version: Linux kernel 6.16.2. Check the vendor advisory for mitigations.

References

• https://git.kernel.org/stable/c/078d33c95bf534d37aa04269d1ae6158e20082d5
• https://git.kernel.org/stable/c/1492e3dcb2be3aa46d1963da96aa9593e4e4db5a
• https://git.kernel.org/stable/c/64b7684042246e3238464c66894e30ba30c7e851
• https://git.kernel.org/stable/c/9e5021a906532ca16e2aac69c0607711e1c70b1f
• https://git.kernel.org/stable/c/a4d634ded4d3d400f115d84f654f316f249531c9
• https://git.kernel.org/stable/c/b05500444b8eb97644efdd180839a04a706be97c
• https://git.kernel.org/stable/c/bada48ad5b0590e318d0f79636ff62a2ef9f4955
• https://cert-portal.siemens.com/productcert/html/ssa-019113.html
• https://cert-portal.siemens.com/productcert/html/ssa-082556.html
• https://cert-portal.siemens.com/productcert/html/ssa-457936.html

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