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NVD / CVE Program· CNA Linux

CVE-2025-39955: tcp: Clear tcp_sk(sk)->fastopen_rsk in tcp_disconnect().

HighCVSS 7.8 · v3.1—No exploit Fix available

Noroxi assessment

Priority: Monitor (action score 31/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.16% (FIRST EPSS).
  • Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: Linux Linux 17d699727577814198d744d6afe54735c6b54c99, 33a4fdf0b4a25f8ce65380c3b0136b407ca57609, 45c8a6cc2bcd780e634a6ba8e46bffbdf1fc5c01; azl3 kernel 6.6.104.2-4 on Azure Linux 3.0 6.6.112.1-1.

Low priority for now. Upgrade to Linux Linux 17d699727577814198d744d6afe54735c6b54c99, 33a4fdf0b4a25f8ce65380c3b0136b407ca57609, 45c8a6cc2bcd780e634a6ba8e46bffbdf1fc5c01; azl3 kernel 6.6.104.2-4 on Azure Linux 3.0 6.6.112.1-1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

In the Linux kernel, the following vulnerability has been resolved: tcp: Clear tcp_sk(sk)->fastopen_rsk in tcp_disconnect(). syzbot reported the splat below where a socket had tcp_sk(sk)->fastopen_rsk in the TCP_ESTABLISHED state. [0] syzbot reused the server-side TCP Fast Open socket as a new client before the TFO socket completes 3WHS: 1. accept() 2. connect(AF_UNSPEC) 3. connect() to another destination As of accept(), sk->sk_state is TCP_SYN_RECV, and tcp_disconnect() changes it to TCP_CLOSE and makes connect() possible, which restarts timers. Since tcp_disconnect() forgot to clear tcp_sk(sk)->fastopen_rsk, the retransmit timer triggered the warning and the intended packet was not retransmitted. Let's call reqsk_fastopen_remove() in tcp_disconnect(). [0]: WARNING: CPU: 2 PID: 0 at net/ipv4/tcp_timer.c:542 tcp_retransmit_timer (net/ipv4/tcp_timer.c:542 (discriminator 7)) Modules linked in: CPU: 2 UID: 0 PID: 0 Comm: swapper/2 Not tainted 6.17.0-rc5-g201825fb4278 #62 PREEMPT(voluntary) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 RIP: 0010:tcp_retransmit_timer (net/ipv4/tcp_timer.c:542 (discriminator 7)) Code: 41 55 41 54 55 53 48 8b af b8 08 00 00 48 89 fb 48 85 ed 0f 84 55 01 00 00 0f b6 47 12 3c 03 74 0c 0f b6 47 12 3c 04 74 04 90 <0f> 0b 90 48 8b 85 c0 00 00 00 48 89 ef 48 8b 40 30 e8 6a 4f 06 3e RSP: 0018:ffffc900002f8d40 EFLAGS: 00010293 RAX: 0000000000000002 RBX: ffff888106911400 RCX: 0000000000000017 RDX: 0000000002517619 RSI: ffffffff83764080 RDI: ffff888106911400 RBP: ffff888106d5c000 R08: 0000000000000001 R09: ffffc900002f8de8 R10: 00000000000000c2 R11: ffffc900002f8ff8 R12: ffff888106911540 R13: ffff888106911480 R14: ffff888106911840 R15: ffffc900002f8de0 FS: 0000000000000000(0000) GS:ffff88907b768000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f8044d69d90 CR3: 0000000002c30003 CR4: 0000000000370ef0 Call Trace: <IRQ> tcp_write_timer (net/ipv4/tcp_timer.c:738) call_timer_fn (kernel/time/timer.c:1747) __run_timers (kernel/time/timer.c:1799 kernel/time/timer.c:2372) timer_expire_remote (kernel/time/timer.c:2385 kernel/time/timer.c:2376 kernel/time/timer.c:2135) tmigr_handle_remote_up (kernel/time/timer_migration.c:944 kernel/time/timer_migration.c:1035) __walk_groups.isra.0 (kernel/time/timer_migration.c:533 (discriminator 1)) tmigr_handle_remote (kernel/time/timer_migration.c:1096) handle_softirqs (./arch/x86/include/asm/jump_label.h:36 ./include/trace/events/irq.h:142 kernel/softirq.c:580) irq_exit_rcu (kernel/softirq.c:614 kernel/softirq.c:453 kernel/softirq.c:680 kernel/softirq.c:696) sysvec_apic_timer_interrupt (arch/x86/kernel/apic/apic.c:1050 (discriminator 35) arch/x86/kernel/apic/apic.c:1050 (discriminator 35)) </IRQ>

Published
Oct 9, 2025
Updated
Nov 10, 2026
EPSS
0.1% · 5th percentile
CWE
—

Report tools

JSON

Action score

31

Monitor

Low priority for now.

CVSS
31 / 40 · 7.8 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.1%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
total

Vulnrichment: CISA's decision-tree inputs.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
linuxlinux kernel

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

  • Linux Linux

    • 3.7affected
    • 8336886f786fdacbc19b719c1f7ea91eb70706d4 and later · before 7ec092a91ff351dcde89c23e795b73a328274db6affected · git
    • 8336886f786fdacbc19b719c1f7ea91eb70706d4 and later · before a4378dedd6e07e62f2fccb17d78c9665718763d0affected · git
    • 8336886f786fdacbc19b719c1f7ea91eb70706d4 and later · before 33a4fdf0b4a25f8ce65380c3b0136b407ca57609affected · git
    • 8336886f786fdacbc19b719c1f7ea91eb70706d4 and later · before 17d699727577814198d744d6afe54735c6b54c99affected · git
    • 8336886f786fdacbc19b719c1f7ea91eb70706d4 and later · before dfd06131107e7b699ef1e2a24ed2f7d17c917753affected · git
    • 8336886f786fdacbc19b719c1f7ea91eb70706d4 and later · before fa4749c065644af4db496b338452a69a3e5147d9affected · git
    • 8336886f786fdacbc19b719c1f7ea91eb70706d4 and later · before ae313d14b45eca7a6bb29cb9bf396d977e7d28fbaffected · git
    • 8336886f786fdacbc19b719c1f7ea91eb70706d4 and later · before 45c8a6cc2bcd780e634a6ba8e46bffbdf1fc5c01affected · git
    • before 3.7not affected · semver
Affected versions · NVD (8)

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • linux linux kernel3.7 and later · before 5.4.300
  • linux linux kernel5.5 and later · before 5.10.245
  • linux linux kernel5.11 and later · before 5.15.194
  • linux linux kernel5.16 and later · before 6.1.154
  • linux linux kernel6.2 and later · before 6.6.108
  • linux linux kernel6.7 and later · before 6.12.49
  • linux linux kernel6.13 and later · before 6.16.9
  • linux linux kernel6.17

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
AlmaLinux:10kernel-abi-stablelistsbefore 6.12.0-124.13.1.el10_16.12.0-124.13.1.el10_1
AlmaLinux:10kernel-docbefore 6.12.0-124.13.1.el10_16.12.0-124.13.1.el10_1
AlmaLinux:8bpftoolbefore 4.18.0-553.87.1.el8_104.18.0-553.87.1.el8_10
AlmaLinux:8kernelbefore 4.18.0-553.87.1.el8_104.18.0-553.87.1.el8_10
AlmaLinux:8kernel-abi-stablelistsbefore 4.18.0-553.87.1.el8_104.18.0-553.87.1.el8_10
AlmaLinux:8kernel-corebefore 4.18.0-553.87.1.el8_104.18.0-553.87.1.el8_10
AlmaLinux:8kernel-cross-headersbefore 4.18.0-553.87.1.el8_104.18.0-553.87.1.el8_10
AlmaLinux:8kernel-debugbefore 4.18.0-553.87.1.el8_104.18.0-553.87.1.el8_10
AlmaLinux:8kernel-debug-corebefore 4.18.0-553.87.1.el8_104.18.0-553.87.1.el8_10
AlmaLinux:8kernel-debug-develbefore 4.18.0-553.87.1.el8_104.18.0-553.87.1.el8_10
AlmaLinux:8kernel-debug-modulesbefore 4.18.0-553.87.1.el8_104.18.0-553.87.1.el8_10
AlmaLinux:8kernel-debug-modules-extrabefore 4.18.0-553.87.1.el8_104.18.0-553.87.1.el8_10
AlmaLinux:8kernel-develbefore 4.18.0-553.87.1.el8_104.18.0-553.87.1.el8_10
AlmaLinux:8kernel-docbefore 4.18.0-553.87.1.el8_104.18.0-553.87.1.el8_10
AlmaLinux:8kernel-headersbefore 4.18.0-553.87.1.el8_104.18.0-553.87.1.el8_10
AlmaLinux:8kernel-modulesbefore 4.18.0-553.87.1.el8_104.18.0-553.87.1.el8_10
AlmaLinux:8kernel-modules-extrabefore 4.18.0-553.87.1.el8_104.18.0-553.87.1.el8_10
AlmaLinux:8kernel-rtbefore 4.18.0-553.87.1.rt7.428.el8_104.18.0-553.87.1.rt7.428.el8_10
AlmaLinux:8kernel-rt-corebefore 4.18.0-553.87.1.rt7.428.el8_104.18.0-553.87.1.rt7.428.el8_10
AlmaLinux:8kernel-rt-debugbefore 4.18.0-553.87.1.rt7.428.el8_104.18.0-553.87.1.rt7.428.el8_10
AlmaLinux:8kernel-rt-debug-corebefore 4.18.0-553.87.1.rt7.428.el8_104.18.0-553.87.1.rt7.428.el8_10
AlmaLinux:8kernel-rt-debug-develbefore 4.18.0-553.87.1.rt7.428.el8_104.18.0-553.87.1.rt7.428.el8_10
AlmaLinux:8kernel-rt-debug-modulesbefore 4.18.0-553.87.1.rt7.428.el8_104.18.0-553.87.1.rt7.428.el8_10
AlmaLinux:8kernel-rt-debug-modules-extrabefore 4.18.0-553.87.1.rt7.428.el8_104.18.0-553.87.1.rt7.428.el8_10

+96

Same product

linux: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-31431crypto: algif_aead - Revert to operating out-of-placeKEV
    90Now
  • CVE-2022-0847A flaw was found in the way the "flags" member of the new pipe buffer structure was lacking proper initialization in copy_page_to_iter_pipe…KEV
    89Now
  • CVE-2021-22555Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACEKEV
    85Now

Published before and after this one in the same product

  • ← EarlierCVE-2023-53687Oct 7, 2025 · tty: serial: samsung_tty: Fix a memory leak in s3c24xx_serial_getclk() when iterating clk
    22Monitor
  • ← EarlierCVE-2025-39954Oct 9, 2025 · clk: sunxi-ng: mp: Fix dual-divider clock rate readback
    22Monitor
  • Later →CVE-2025-39956Oct 9, 2025 · igc: don't fail igc_probe() on LED setup error
    22Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Linux Linux17d699727577814198d744d6afe54735c6b54c99Vendor (CNA)
Linux Linux33a4fdf0b4a25f8ce65380c3b0136b407ca57609Vendor (CNA)
Linux Linux45c8a6cc2bcd780e634a6ba8e46bffbdf1fc5c01Vendor (CNA)
Linux Linux7ec092a91ff351dcde89c23e795b73a328274db6Vendor (CNA)
Linux Linuxa4378dedd6e07e62f2fccb17d78c9665718763d0Vendor (CNA)
Linux Linuxae313d14b45eca7a6bb29cb9bf396d977e7d28fbVendor (CNA)
Linux Linuxdfd06131107e7b699ef1e2a24ed2f7d17c917753Vendor (CNA)
Linux Linuxfa4749c065644af4db496b338452a69a3e5147d9Vendor (CNA)
azl3 kernel 6.6.104.2-4 on Azure Linux 3.06.6.112.1-1 · CBL-Mariner ReleasesMicrosoft (MSRC)
almalinux:kernel-abi-stablelists6.12.0-124.13.1.el10_1 · AlmaLinux:10Package registry (OSV)
almalinux:kernel-doc6.12.0-124.13.1.el10_1 · AlmaLinux:10Package registry (OSV)
almalinux:kernel-rt4.18.0-553.87.1.rt7.428.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-rt-core4.18.0-553.87.1.rt7.428.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-rt-debug4.18.0-553.87.1.rt7.428.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-rt-debug-core4.18.0-553.87.1.rt7.428.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-rt-debug-devel4.18.0-553.87.1.rt7.428.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-rt-debug-modules4.18.0-553.87.1.rt7.428.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-rt-debug-modules-extra4.18.0-553.87.1.rt7.428.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-rt-devel4.18.0-553.87.1.rt7.428.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-rt-modules4.18.0-553.87.1.rt7.428.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-rt-modules-extra4.18.0-553.87.1.rt7.428.el8_10 · AlmaLinux:8Package registry (OSV)
debian:linux6.1.158-1 · Debian:12Package registry (OSV)
debian:linux-6.16.1.158-1~deb11u1 · Debian:11Package registry (OSV)
opensuse:dtb-aarch646.12.0-160000.7.1 · openSUSE:Leap 16.0Package registry (OSV)
opensuse:kernel-64kb6.12.0-160000.7.1 · openSUSE:Leap 16.0Package registry (OSV)
opensuse:kernel-default6.12.0-160000.7.1 · openSUSE:Leap 16.0Package registry (OSV)
opensuse:kernel-default-base6.12.0-160000.6.1.160000.2.4 · openSUSE:Leap 16.0Package registry (OSV)
opensuse:kernel-docs6.12.0-160000.7.1 · openSUSE:Leap 16.0Package registry (OSV)
opensuse:kernel-kvmsmall6.12.0-160000.7.1 · openSUSE:Leap 16.0Package registry (OSV)
opensuse:kernel-obs-build6.12.0-160000.7.1 · openSUSE:Leap 16.0Package registry (OSV)

+30

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

Not on record for this CVE: EPSS history · patch commit or PR link · researcher credit · variant or chain candidate · public bounty program.

Technical details

Attack conditions

  • Someone with local access to the system can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

—

CVSS vector

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

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

References

Show all references (9 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records