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Linux KernelOperating system · Linux

CVE-2026-31665

HIGH · 7.8 CVSS v3.1 Published 2026-04-24
Fix available
A fix is available. Upgrade to 5.10.253 / 5.15.203 or later.
See remediation →
80/100
Remediation priority · High
Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
In the Linux kernel, the following vulnerability has been resolved: netfilter: nft_ct: fix use-after-free in timeout object destroy nft_ct_timeout_obj_destroy() frees the timeout object with kfree() immediately after nf_ct_untimeout(), without waiting for an RCU grace period. Concurrent packet processing on other CPUs may still hold RCU-protected references to the timeout object obtained via rcu_dereference() in nf_ct_timeout_data(). Add an rcu_head to struct nf_ct_timeout and use kfree_rcu() to defer freeing until after an RCU grace period, matching the approach already used in nfnetlink_cttimeout.c. KASAN report: BUG: KASAN: slab-use-after-free in nf_conntrack_tcp_packet+0x1381/0x29d0 Read of size 4 at addr ffff8881035fe19c by task exploit/80 Call Trace: nf_conntrack_tcp_packet+0x1381/0x29d0 nf_conntrack_in+0x612/0x8b0 nf_hook_slow+0x70/0x100 __ip_local_out+0x1b2/0x210 tcp_sendmsg_locked+0x722/0x1580 __sys_sendto+0x2d8/0x320 Allocated by task 75: nft_ct_timeout_obj_init+0xf6/0x290 nft_obj_init+0x107/0x1b0 nf_tables_newobj+0x680/0x9c0 nfnetlink_rcv_batch+0xc29/0xe00 Freed by task 26: nft_obj_destroy+0x3f/0xa0 nf_tables_trans_destroy_work+0x51c/0x5c0 process_one_work+0x2c4/0x5a0

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis
How this class of weakness works · CWE-416

Memory is used after it has been freed, so its contents — now potentially attacker-controlled — drive the program's behaviour. With careful heap grooming this becomes code execution. The fix requires disciplined ownership of memory and often a targeted rework of the object lifecycle.

General guidance for the use after free class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Linux KernelOperating system
Affected:>= 4.19.1, < 5.10.253>= 5.11, < 5.15.203>= 5.16, < 6.1.169>= 6.2, < 6.6.135>= 6.7, < 6.12.82>= 6.13, < 6.18.23>= 6.19, < 6.19.13= 4.19= 7.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 5.10.253 / 5.15.203 / 6.1.169 or later
Fixed in 5.10.2535.15.2036.1.169
Vendor patch git.kernel.org →
Recommended fix High confidence

Upgrade to kernel 5.10.253+, 5.15.203+, 6.1.169+, or 6.6.135+ (whichever branch you are on)

  1. Identify the current running kernel version using `uname -r`
  2. Determine which version range your current kernel falls into from the affected versions: 4.19.1 to 5.10.252, 5.11 to 5.15.202, 5.16 to 6.1.168, or 6.2 to 6.6.134
  3. Upgrade to a kernel version >= 5.10.253 (for 5.x branches), >= 5.15.203 (for 5.11-5.15 branches), >= 6.1.169 (for 5.16-6.1 branches), or >= 6.6.135 (for 6.2+ branches)
  4. On Debian/Ubuntu: `apt-get update && apt-get upgrade linux-image-generic`
  5. On RHEL/CentOS: `yum update kernel`
  6. On Fedora: `dnf update kernel`
  7. Reboot into the new kernel using `reboot`
  8. Verify the fix is applied by checking the kernel version and confirming the commit is included
Caveat Kernel upgrades may require system reboot and could introduce compatibility issues with out-of-tree kernel modules or custom drivers; ensure backup and test in staging first

Generated from the published advisory — verify against the referenced sources before acting.

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $3,200. Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-31665 in production — separate from our analysis above.

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What this is

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  • Version or environment caveats, and links to real fixes
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