CVE-2026-23139
Published: 14 February 2026
Summary
CVE-2026-23139 is a high-severity an unspecified weakness vulnerability in Linux Linux Kernel. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Application or System Exploitation (T1499.004); ranked at the 11.2th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SC-5 (Denial-of-service Protection) and SC-6 (Resource Availability).
Deeper analysis
CVE-2026-23139 is a vulnerability in the Linux kernel's netfilter nf_conncount component, which handles connection counting and garbage collection (GC) for network connections. The issue stems from the last_gc timestamp being updated every time a new connection is tracked, even if GC is not performed. This allows high packet rates to perpetually bypass GC, causing the connection tracking list to grow indefinitely and exhaust system resources.
A remote, unauthenticated attacker can exploit this vulnerability over the network with low complexity and no user interaction, as indicated by its CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H). By generating a sufficiently high rate of packets that trigger new connection tracking, the attacker prevents GC from running, leading to unbounded memory consumption in the conntrack table and potential denial-of-service through resource exhaustion.
Mitigation involves applying the relevant stable kernel patches, as detailed in the upstream commit references. These include fixes such as https://git.kernel.org/stable/c/26a82dce2beee39c43c109d9647e16f49cb02a35, which update the last_gc value only after GC has actually been performed, ensuring proper list management under high load. Security practitioners should update affected Linux kernels to versions incorporating these commits.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-5898
Vulnerability details
In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_conncount: update last_gc only when GC has been performed Currently last_gc is being updated everytime a new connection is tracked, that means that it is updated even if a…
more
GC wasn't performed. With a sufficiently high packet rate, it is possible to always bypass the GC, causing the list to grow infinitely. Update the last_gc value only when a GC has been actually performed.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
The vulnerability is a kernel flaw in nf_conncount allowing remote high-rate packet floods to bypass GC and exhaust conntrack memory, directly enabling Endpoint DoS via system exploitation.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Directly mitigates the vulnerability by requiring timely remediation through application of Linux kernel patches that fix the improper last_gc timestamp update.
Implements denial-of-service protections such as network rate limiting to block high packet rates that bypass garbage collection in the nf_conncount component.
Enforces resource allocation controls like limiting the nf_conntrack_max table size to prevent unbounded memory growth from uncollected connections.