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EUVD-2026-345868

European Vulnerability Database identifier assigned by ENISA

Reserved

2026-10-02 08:05

Assigner

ENISA

Alias of

a CVE record, shown under related vulnerabilities. This identifier carries no description, severity or references of its own: they belong to that CVE.

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{
  "assigner": "ENISA",
  "date_reserved": "2026-10-02T08:05:30.999717+00:00",
  "id": "EUVD-2026-345868"
}

CVE-2024-40910 (GCVE-0-2024-40910)

Vulnerability from cvelistv5 – Published: 2024-07-12 12:20 – Updated: 2026-08-05 11:33

Title

ax25: Fix refcount imbalance on inbound connections

Summary

In the Linux kernel, the following vulnerability has been resolved: ax25: Fix refcount imbalance on inbound connections When releasing a socket in ax25_release(), we call netdev_put() to decrease the refcount on the associated ax.25 device. However, the execution path for accepting an incoming connection never calls netdev_hold(). This imbalance leads to refcount errors, and ultimately to kernel crashes. A typical call trace for the above situation will start with one of the following errors: refcount_t: decrement hit 0; leaking memory. refcount_t: underflow; use-after-free. And will then have a trace like: Call Trace: <TASK> ? show_regs+0x64/0x70 ? __warn+0x83/0x120 ? refcount_warn_saturate+0xb2/0x100 ? report_bug+0x158/0x190 ? prb_read_valid+0x20/0x30 ? handle_bug+0x3e/0x70 ? exc_invalid_op+0x1c/0x70 ? asm_exc_invalid_op+0x1f/0x30 ? refcount_warn_saturate+0xb2/0x100 ? refcount_warn_saturate+0xb2/0x100 ax25_release+0x2ad/0x360 __sock_release+0x35/0xa0 sock_close+0x19/0x20 [...] On reboot (or any attempt to remove the interface), the kernel gets stuck in an infinite loop: unregister_netdevice: waiting for ax0 to become free. Usage count = 0 This patch corrects these issues by ensuring that we call netdev_hold() and ax25_dev_hold() for new connections in ax25_accept(). This makes the logic leading to ax25_accept() match the logic for ax25_bind(): in both cases we increment the refcount, which is ultimately decremented in ax25_release().

Severity

8.8 (High)


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

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2024-09-10 17:06 UTC

Assigner

Linux mitre root Scorecard

References

5 references

URL	Tags
https://git.kernel.org/stable/c/f4df9d6c8d4e4c818…
https://git.kernel.org/stable/c/52100fd74ad07b53a…
https://git.kernel.org/stable/c/a723a6c8d4831cc8e…
https://git.kernel.org/stable/c/3c34fb0bd4a423759…
https://lists.debian.org/debian-lts-announce/2025…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: 9fd75b66b8f68498454d685dc4ba13192ae069b0 , < f4df9d6c8d4e4c818252b0419c2165d66eabd4eb (git) Affected: 9fd75b66b8f68498454d685dc4ba13192ae069b0 , < 52100fd74ad07b53a4666feafff1cd11436362d3 (git) Affected: 9fd75b66b8f68498454d685dc4ba13192ae069b0 , < a723a6c8d4831cc8e2c7b0c9f3f0c010d4671964 (git) Affected: 9fd75b66b8f68498454d685dc4ba13192ae069b0 , < 3c34fb0bd4a4237592c5ecb5b2e2531900c55774 (git) Affected: c44a453ffe16eb08acdc6129ac4fa0192dbc0456 (git) Affected: de55a1338e6a48ff1e41ea8db1432496fbe2a62b (git) Affected: 9e1e088a57c23251f1cfe9601bbd90ade2ea73b9 (git) Affected: b20a5ab0f5fb175750c6bafd4cf12daccf00c738 (git) Affected: 452ae92b99062d2f6a34324eaf705a3b7eac9f8b (git) Affected: 534156dd4ed768e30a43de0036f45dca7c54818f (git) Affected: 4.14.277 , < 4.15 (semver) Affected: 4.19.240 , < 4.20 (semver) Affected: 5.4.190 , < 5.5 (semver) Affected: 5.10.112 , < 5.11 (semver) Affected: 5.15.35 , < 5.16 (semver) Affected: 5.17.2 , < 5.18 (semver)
Linux	Linux	Affected: 5.18 Unaffected: 0 , < 5.18 (semver) Unaffected: 6.1.95 , ≤ 6.1.* (semver) Unaffected: 6.6.35 , ≤ 6.6.* (semver) Unaffected: 6.9.6 , ≤ 6.9.* (semver) Unaffected: 6.10 , ≤ * (original_commit_for_fix)

Show details on NVD website

JSON

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                "id": "CVE-2024-40910",
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              "value": "AV:A - The imbalance is created by an inbound SABM processed in `ax25_rcv()`, reached from the link-layer handlers `ax25_kiss_rcv()` (RF/KISS TNC, 6pack, scc) and `bpq_rcv()` (AX.25 encapsulated in Ethernet, ethertype 0x08FF), so any station on the shared radio channel or the local Ethernet segment can trigger it. AX.25 frames are not IP-routable by the kernel itself, so this is adjacent rather than full network reach.\nAC:L - The attacker simply connects and disconnects repeatedly; each accepted-then-closed session deterministically drops one unheld netdev reference and one unheld ax25_dev reference, and only a couple of iterations are needed to drive `ax25_dev-\u003erefcount` to zero. No race, no memory-layout precondition, and the attacker controls the repetition count.\nPR:N - AX.25 has no authentication whatsoever \u2014 an unauthenticated remote station only needs to send a SABM to a listening callsign on a node/BBS/ax25d service. No credentials or local account on the victim are required.\nUI:N - A listening AX.25 service accepts inbound connections automatically and closes the session socket when the peer disconnects, which is exactly the release path that performs the unbalanced `netdev_put()`/`ax25_dev_put()`. No operator action is needed.\nS:U - The corruption is confined to kernel memory within the same security authority; no VM, IOMMU, or sandbox boundary is crossed.\nC:H - `ax25_dev_put()` frees the `ax25_dev` while `dev-\u003eax25_ptr` and `ax25_dev_list` still reference it, so subsequent received frames read attacker-refillable freed slab memory (`values[]`, `forward`, `sysheader`), and the netdev refcount underflow can free `struct net_device` while sockets still point at it \u2014 a use-after-free that is leverageable for kernel memory disclosure.\nI:H - The freed `ax25_dev` embeds a `timer_list` (DAMA slave timer with a function pointer) and a `list_head` that are still armed/linked, plus a `net_device *forward` used on the transmit path; reclaiming the slab yields write and control-flow-hijack primitives typical of a use-after-free.\nA:H - The commit documents kernel crashes from the refcount underflow, and on interface teardown or reboot the kernel spins forever in `unregister_netdevice: waiting for ax0 to become free. Usage count = 0` with RTNL held \u2014 a permanent, remotely inducible hang in addition to the UAF oops."
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Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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EUVD-2026-345868

CVE-2024-40910 (GCVE-0-2024-40910)

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