7.8

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

Modified
AliasesUBUNTU-CVE-2025-39955DEBIAN-CVE-2025-39955
Published 09-10-2025Last modified 15-10-2026

Vulnerability summary

CVE-2025-39955 is a high (CVSS 7.8) vulnerability in linux. EPSS estimates a 0.17% chance of exploitation in the next 30 days, higher than 5.7% of scored vulnerabilities.

Priority
Routine

Not severe (CVSS 7.8, local access); no exploitation reported by the 5 checked sources

Source freshness unavailable

How is this decided?
CVSS score
7.8/10
010
High · v3.1 (NVD)
EPSS score
0.17%
0%100%
Low · +0.01 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 62 · Related 40
DLA-4379-1DLA-4404-1DSA-6053-1MGASA-2025-0309MGASA-2025-0310OPENSUSE-SU-2025:20091-1

Timeline

  1. 09-10-2025
    PublishedVulnerability first disclosed.
  2. 15-10-2026
    Last modifiedVulnerability information updated.

Description

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>

CVSS metrics

4 scores · 3 sources · 2 versions

EPSS trend

Probability

0.17%

Chance of exploitation in the next 30 days

Percentile

6%

Versus all other CVEs

30-day change

Increase +0.01 pp

From 0.16% on 04-10-2026

04-10-202603-11-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

No weakness data has been published for this record.

Affected systems

Version check

Known conditions: local access, low-privilege account, no user interaction (CVSS vector). Other conditions: not stated in public data.

Ubuntu148 products
  • linuxAll versions (No fix recorded) | < 5.15.0-170.180 | < 6.8.0-106.106
  • linux-allwinner-5.19All versions (No fix recorded)
  • linux-awsAll versions (No fix recorded) | < 5.15.0-1100.107 | < 6.8.0-1050.53
  • linux-aws-5.0All versions (No fix recorded)
  • linux-aws-5.11All versions (No fix recorded)
Linux2 products
  • linux≥ 8336886f786fdacbc19b719c1f7ea91eb70706d4, < 7ec092a91ff351dcde89c23e795b73a328274db6 | ≥ 8336886f786fdacbc19b719c1f7ea91eb70706d4, < a4378dedd6e07e62f2fccb17d78c9665718763d0 | ≥ 8336886f786fdacbc19b719c1f7ea91eb70706d4, < 33a4fdf0b4a25f8ce65380c3b0136b407ca57609 | ≥ 8336886f786fdacbc19b719c1f7ea91eb70706d4, < 17d699727577814198d744d6afe54735c6b54c99 | ≥ 8336886f786fdacbc19b719c1f7ea91eb70706d4, < dfd06131107e7b699ef1e2a24ed2f7d17c917753 | ≥ 8336886f786fdacbc19b719c1f7ea91eb70706d4, < fa4749c065644af4db496b338452a69a3e5147d9 | ≥ 8336886f786fdacbc19b719c1f7ea91eb70706d4, < ae313d14b45eca7a6bb29cb9bf396d977e7d28fb | ≥ 8336886f786fdacbc19b719c1f7ea91eb70706d4, < 45c8a6cc2bcd780e634a6ba8e46bffbdf1fc5c01 | 3.7
  • linux_kernel≥ 3.7, < 5.4.300 | ≥ 5.5, < 5.10.245 | ≥ 5.11, < 5.15.194 | ≥ 5.16, < 6.1.154 | ≥ 6.2, < 6.6.108 | ≥ 6.7, < 6.12.49 | ≥ 6.13, < 6.16.9 | 6.17:rc1 | 6.17:rc2 | 6.17:rc3 | 6.17:rc4 | 6.17:rc5 | 6.17:rc6
Debian1 product
  • linux< 6.1.158-1 | < 6.12.57-1 | < 6.16.9-1

3 vendors · 151 products

References

38 links
Show all 38 references