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NVD / CVE Program· CNA Linux

CVE-2025-40186: tcp: Don't call reqsk_fastopen_remove() in tcp_conn_request().

Noroxi assessment

Priority: Monitor (action score 32/100)

  • 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: 0.58% (FIRST EPSS).
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. Special conditions such as timing or configuration are required.
  • Fixed version: Linux Linux 2e7cbbbe3d61c63606994b7ff73c72537afe2e1c, 422c1c173c39bbbae1e0eaaf8aefe40b2596233b, 5.10.246.

Low priority for now. Upgrade to Linux Linux 2e7cbbbe3d61c63606994b7ff73c72537afe2e1c, 422c1c173c39bbbae1e0eaaf8aefe40b2596233b, 5.10.246 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: Don't call reqsk_fastopen_remove() in tcp_conn_request(). syzbot reported the splat below in tcp_conn_request(). [0] If a listener is close()d while a TFO socket is being processed in tcp_conn_request(), inet_csk_reqsk_queue_add() does not set reqsk->sk and calls inet_child_forget(), which calls tcp_disconnect() for the TFO socket. After the cited commit, tcp_disconnect() calls reqsk_fastopen_remove(), where reqsk_put() is called due to !reqsk->sk. Then, reqsk_fastopen_remove() in tcp_conn_request() decrements the last req->rsk_refcnt and frees reqsk, and __reqsk_free() at the drop_and_free label causes the refcount underflow for the listener and double-free of the reqsk. Let's remove reqsk_fastopen_remove() in tcp_conn_request(). Note that other callers make sure tp->fastopen_rsk is not NULL. [0]: refcount_t: underflow; use-after-free. WARNING: CPU: 12 PID: 5563 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28) Modules linked in: CPU: 12 UID: 0 PID: 5563 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025 RIP: 0010:refcount_warn_saturate (lib/refcount.c:28) Code: ab e8 8e b4 98 ff 0f 0b c3 cc cc cc cc cc 80 3d a4 e4 d6 01 00 75 9c c6 05 9b e4 d6 01 01 48 c7 c7 e8 df fb ab e8 6a b4 98 ff <0f> 0b e9 03 5b 76 00 cc 80 3d 7d e4 d6 01 00 0f 85 74 ff ff ff c6 RSP: 0018:ffffa79fc0304a98 EFLAGS: 00010246 RAX: d83af4db1c6b3900 RBX: ffff9f65c7a69020 RCX: d83af4db1c6b3900 RDX: 0000000000000000 RSI: 00000000ffff7fff RDI: ffffffffac78a280 RBP: 000000009d781b60 R08: 0000000000007fff R09: ffffffffac6ca280 R10: 0000000000017ffd R11: 0000000000000004 R12: ffff9f65c7b4f100 R13: ffff9f65c7d23c00 R14: ffff9f65c7d26000 R15: ffff9f65c7a64ef8 FS: 00007f9f962176c0(0000) GS:ffff9f65fcf00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000200000000180 CR3: 000000000dbbe006 CR4: 0000000000372ef0 Call Trace: <IRQ> tcp_conn_request (./include/linux/refcount.h:400 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 ./include/net/sock.h:1965 ./include/net/request_sock.h:131 net/ipv4/tcp_input.c:7301) tcp_rcv_state_process (net/ipv4/tcp_input.c:6708) tcp_v6_do_rcv (net/ipv6/tcp_ipv6.c:1670) tcp_v6_rcv (net/ipv6/tcp_ipv6.c:1906) ip6_protocol_deliver_rcu (net/ipv6/ip6_input.c:438) ip6_input (net/ipv6/ip6_input.c:500) ipv6_rcv (net/ipv6/ip6_input.c:311) __netif_receive_skb (net/core/dev.c:6104) process_backlog (net/core/dev.c:6456) __napi_poll (net/core/dev.c:7506) net_rx_action (net/core/dev.c:7569 net/core/dev.c:7696) handle_softirqs (kernel/softirq.c:579) do_softirq (kernel/softirq.c:480) </IRQ>

HighCVSS 8.1 · v3.1—No exploit Fix available
Published
Nov 12, 2025
Updated
Oct 19, 2026
EPSS
0.5% · 47th percentile
CWE
—

Report tools

JSON

Action score

32

Monitor

Low priority for now.

CVSS
32 / 40 · 8.1 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.5%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
total

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · Linux
8.1
NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

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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.

—

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

    • ae313d14b45eca7a6bb29cb9bf396d977e7d28fb, 6.17affected
    • 7ec092a91ff351dcde89c23e795b73a328274db6 and later · before e359b742eac1eac75cff4e38ee2e8cea492acd9baffected · git
    • a4378dedd6e07e62f2fccb17d78c9665718763d0 and later · before ff6a8883f96a5bc74241ce5b3d431a6dcfa2124daffected · git
    • 33a4fdf0b4a25f8ce65380c3b0136b407ca57609 and later · before eb85ad5f23268d64b037bfb545cbcba3752f90c7affected · git
    • 17d699727577814198d744d6afe54735c6b54c99 and later · before 643a94b0cf767325e953591c212be2eb826b9d7faffected · git
    • dfd06131107e7b699ef1e2a24ed2f7d17c917753 and later · before 422c1c173c39bbbae1e0eaaf8aefe40b2596233baffected · git
    • fa4749c065644af4db496b338452a69a3e5147d9 and later · before c11ace909e873118295e9eb22dc8c58b0b50eb32affected · git
    • 45c8a6cc2bcd780e634a6ba8e46bffbdf1fc5c01 and later · before 64dc47a13aa3d9daf7cec29b44dca8e22a6aea15affected · git
    • 45c8a6cc2bcd780e634a6ba8e46bffbdf1fc5c01 and later · before 2e7cbbbe3d61c63606994b7ff73c72537afe2e1caffected · git
    • 5.4.300 and later · before 5.4.301affected · semver

Package-level exposure

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

EcosystemPackageAffected rangeFix
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
AlmaLinux:8kernel-rt-develbefore 4.18.0-553.87.1.rt7.428.el8_104.18.0-553.87.1.rt7.428.el8_10
AlmaLinux:8kernel-rt-modulesbefore 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-2026-74705udp: fix potential use-after-free in tunnel segmentation
    40Plan
  • CVE-2026-74612veth: fix skb length accounting after XDP frag adjustment
    40Plan
  • CVE-2026-74475vxlan: use neigh_ha_snapshot() in route_shortcircuit()
    40Plan

Published before and after this one in the same product

  • ← EarlierCVE-2025-40184Nov 12, 2025 · KVM: arm64: Fix debug checking for np-guests using huge mappings
    0Monitor
  • ← EarlierCVE-2025-40185Nov 12, 2025 · ice: ice_adapter: release xa entry on adapter allocation failure
    0Monitor
  • Later →CVE-2025-40187Nov 12, 2025 · net/sctp: fix a null dereference in sctp_disposition sctp_sf_do_5_1D_ce()
    30Monitor

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 Linux2e7cbbbe3d61c63606994b7ff73c72537afe2e1cVendor (CNA)
Linux Linux422c1c173c39bbbae1e0eaaf8aefe40b2596233bVendor (CNA)
Linux Linux5.10.246Vendor (CNA)
Linux Linux5.15.195Vendor (CNA)
Linux Linux5.4.301Vendor (CNA)
Linux Linux6.1.157Vendor (CNA)
Linux Linux6.12.54Vendor (CNA)
Linux Linux6.17Vendor (CNA)
Linux Linux6.6.113Vendor (CNA)
Linux Linux643a94b0cf767325e953591c212be2eb826b9d7fVendor (CNA)
Linux Linux64dc47a13aa3d9daf7cec29b44dca8e22a6aea15Vendor (CNA)
Linux Linuxc11ace909e873118295e9eb22dc8c58b0b50eb32Vendor (CNA)
Linux Linuxe359b742eac1eac75cff4e38ee2e8cea492acd9bVendor (CNA)
Linux Linuxeb85ad5f23268d64b037bfb545cbcba3752f90c7Vendor (CNA)
Linux Linuxff6a8883f96a5bc74241ce5b3d431a6dcfa2124dVendor (CNA)
almalinux:bpftool4.18.0-553.87.1.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel4.18.0-553.87.1.el8_10 · AlmaLinux:8Package 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)
red hat:kernel-rt0:4.18.0-553.87.1.rt7.428.el8_10 · Red Hat:enterprise_linux:8::nfvPackage registry (OSV)
red hat:kernel-rt-core0:4.18.0-553.87.1.rt7.428.el8_10 · Red Hat:enterprise_linux:8::nfvPackage registry (OSV)

+22

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.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • Special conditions such as timing or configuration are required.

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
Network
Attack complexity
High
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

—

CVSS vector

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

nvd-secondary

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.

Change log

  1. SSVC exploitation— → none
  2. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (7 more)

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

All records