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Linux KernelOperating system · Linux

CVE-2026-53260

CRITICAL · 9.8 CVSS v3.1 Published 2026-06-25
Fix available
A fix is available. Upgrade to 7.0.13 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click Patch available 8 weeks old

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: tcp: Add preempt_{disable,enable}_nested() in reqsk_queue_hash_req(). syzbot reported a weird reqsk->rsk_refcnt underflow in __inet_csk_reqsk_queue_drop(). The captured reqsk_put() in __inet_csk_reqsk_queue_drop() is called only when it successfully removes reqsk from ehash. Moreover, reqsk_timer_handler() calls another reqsk_put() after that. This indicates that the reqsk was missing both refcnts for ehash and the timer itself. Since all the syzbot reports had PREEMPT_RT enabled, the only possible scenario is that reqsk_queue_hash_req() is preempted after mod_timer() and before refcount_set(), and then the timer triggered after 1s aborts the reqsk due to its listener's close(). Let's wrap mod_timer() and refcount_set() with preempt_disable_nested() and preempt_enable_nested(). Note that inet_ehash_insert() holds the normal spin_lock() (mutex in PREEMPT_RT), so it must be called outside of preempt_disable_nested(), but this is fine. The lookup path just ignores 0 sk_refcnt entries in ehash and tries to create another reqsk, but this will fail at inet_ehash_insert(). [0]: refcount_t: underflow; use-after-free. WARNING: lib/refcount.c:28 at refcount_warn_saturate+0xb2/0x110 lib/refcount.c:28, CPU#0: ktimers/0/16 Modules linked in: CPU: 0 UID: 0 PID: 16 Comm: ktimers/0 Tainted: G L syzkaller #0 PREEMPT_{RT,(full)} Tainted: [L]=SOFTLOCKUP Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026 RIP: 0010:refcount_warn_saturate+0xb2/0x110 lib/refcount.c:28 Code: e4 7d d1 0a 67 48 0f b9 3a eb 4a e8 38 3d 23 fd 48 8d 3d e1 7d d1 0a 67 48 0f b9 3a eb 37 e8 25 3d 23 fd 48 8d 3d de 7d d1 0a <67> 48 0f b9 3a eb 24 e8 12 3d 23 fd 48 8d 3d db 7d d1 0a 67 48 0f RSP: 0000:ffffc90000157948 EFLAGS: 00010246 RAX: ffffffff84a1301b RBX: 0000000000000003 RCX: ffff88801ca98000 RDX: 0000000000000100 RSI: 0000000000000000 RDI: ffffffff8f72ae00 RBP: ffffffff99ae3b01 R08: ffff88801ca98000 R09: 0000000000000005 R10: 0000000000000100 R11: 0000000000000004 R12: ffff8880425ef568 R13: ffff8880425ef4f8 R14: ffff8880425ef578 R15: 0000000000000000 FS: 0000000000000000(0000) GS:ffff888126386000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f7b46710e9c CR3: 000000000dbb6000 CR4: 00000000003526f0 Call Trace: <TASK> __refcount_sub_and_test include/linux/refcount.h:400 [inline] __refcount_dec_and_test include/linux/refcount.h:432 [inline] refcount_dec_and_test include/linux/refcount.h:450 [inline] reqsk_put include/net/request_sock.h:136 [inline] __inet_csk_reqsk_queue_drop+0x3ce/0x440 net/ipv4/inet_connection_sock.c:1007 reqsk_timer_handler+0x651/0xdf0 net/ipv4/inet_connection_sock.c:1137 call_timer_fn+0x192/0x5e0 kernel/time/timer.c:1748 expire_timers kernel/time/timer.c:1799 [inline] __run_timers kernel/time/timer.c:2374 [inline] __run_timer_base+0x6a3/0x9f0 kernel/time/timer.c:2386 run_timer_base kernel/time/timer.c:2395 [inline] run_timer_softirq+0x67/0x170 kernel/time/timer.c:2403 handle_softirqs+0x1de/0x6d0 kernel/softirq.c:622 __do_softirq kernel/softirq.c:656 [inline] run_ktimerd+0x69/0x100 kernel/softirq.c:1151 smpboot_thread_fn+0x541/0xa50 kernel/smpboot.c:160 kthread+0x388/0x470 kernel/kthread.c:436 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 </TASK>

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 · high confidence

A race condition in Linux kernel's TCP request socket handling (reqsk_queue_hash_req()) causes a refcount underflow when PREEMPT_RT is enabled. The function can be preempted between mod_timer() and refcount_set(), allowing the timer to fire and decrement the refcount twice - once in the timer handler and once during ehash removal - resulting in an underflow and use-after-free.

MitigationApply the upstream kernel patch that wraps mod_timer() and refcount_set() with preempt_disable_nested()/preempt_enable_nested(), ensuring atomic timer registration. For systems not using PREEMPT_RT, the race window is much smaller but the fix should still be applied for defense-in-depth.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

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:>= 6.12, < 7.0.13= 7.1

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
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check kernel version
    Run 'uname -r' or 'cat /proc/version' and compare the version to the affected ranges: >= 6.12, < 7.0.13, or = 7.1
    Affected if Kernel version falls within the affected ranges AND PREEMPT_RT is enabled
  2. Check if PREEMPT_RT is enabled
    Examine the kernel command line in /proc/cmdline for 'preempt=full' or 'preempt_rt' or 'PREEMPT_RT'. Alternatively, check the kernel config via 'cat /boot/config-$(uname -r) | grep CONFIG_PREEMPT_RT' or 'zcat /proc/config.gz | grep CONFIG_PREEMPT_RT' if available
    Affected if PREEMPT_RT is enabled (CONFIG_PREEMPT_RT=y or preempt=full/preempt_rt on cmdline)
  3. Verify TCP listening sockets are in use
    Run 'ss -ltn' or 'netstat -ltn' to list active TCP listening sockets. The vulnerability triggers when reqsk_queue_hash_req() is called during connection establishment
    Affected if The system accepts TCP connections and the kernel is in the affected version range with PREEMPT_RT
  4. Confirm TCP request socket hash table is in use
    Check /proc/net/sockstat or /proc/net/sockstat6 for request socket allocation, or monitor for connection attempts to listening ports
    Affected if TCP connections are being accepted and the kernel is vulnerable (affected version + PREEMPT_RT)

A system is affected if it runs a Linux kernel version 6.12 through 7.0.12, 7.1, or any version >= 7.2 that backports the vulnerable code, with PREEMPT_RT enabled (CONFIG_PREEMPT_RT=y or preempt=full/preempt_rt kernel parameter), and accepts TCP connections.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 7.0.13 or later
Fixed in 7.0.13
Vendor patch git.kernel.org →
Interim mitigation

Apply the upstream kernel patch that wraps mod_timer() and refcount_set() with preempt_disable_nested()/preempt_enable_nested(), ensuring atomic timer registration. For systems not using PREEMPT_RT, the race window is much smaller but the fix should still be applied for defense-in-depth.

Recommended fix High confidence

Linux Kernel 7.0.13+ or 7.2+ (depending on which major.minor branch you are on)

  1. 1. Identify the current running kernel version using `uname -r` or `cat /proc/version`
  2. 2. If running kernel 6.12.x through 7.0.12: Plan to upgrade to kernel 7.0.13 or later in the 7.0.x stable series
  3. 3. If running kernel 7.1.x: Plan to upgrade to kernel 7.2 or later in the 7.x stable series
  4. 4. Obtain the updated kernel from your Linux distribution's package repositories or kernel.org (https://www.kernel.org/)
  5. 5. Apply the kernel upgrade following your distribution's standard procedures (e.g., `apt-get dist-upgrade`, `yum update`, or manual installation)
  6. 6. Reboot the system into the updated kernel
  7. 7. Verify the new kernel version is running with `uname -r`

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

Fix this in Linux Kernel Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing4.0 h
  • Review / QA1.0 h
9.0 hours of engineering $1,540
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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-2026-53260 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
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