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

Vulnerability from cvelistv5 – Published: 2024-07-12 12:20 – Updated: 2026-08-05 11:33
VLAI
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
References
Impacted products
Vendor Product Version CPE status
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)
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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)
guessed Create a notification for this product.
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                  "content": {
                    "id": "CVE-2024-40910",
                    "options": [
                      {
                        "Exploitation": "none"
                      },
                      {
                        "Automatable": "no"
                      },
                      {
                        "Technical Impact": "partial"
                      }
                    ],
                    "role": "CISA Coordinator",
                    "timestamp": "2024-09-10T17:06:05.854978Z",
                    "version": "2.0.3"
                  },
                  "type": "ssvc"
                }
              }
            ],
            "providerMetadata": {
              "dateUpdated": "2024-09-11T12:42:24.847Z",
              "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "shortName": "CISA-ADP"
            },
            "title": "CISA ADP Vulnrichment"
          }
        ],
        "cna": {
          "affected": [
            {
              "defaultStatus": "unaffected",
              "product": "Linux",
              "programFiles": [
                "net/ax25/af_ax25.c"
              ],
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "vendor": "Linux",
              "versions": [
                {
                  "lessThan": "f4df9d6c8d4e4c818252b0419c2165d66eabd4eb",
                  "status": "affected",
                  "version": "9fd75b66b8f68498454d685dc4ba13192ae069b0",
                  "versionType": "git"
                },
                {
                  "lessThan": "52100fd74ad07b53a4666feafff1cd11436362d3",
                  "status": "affected",
                  "version": "9fd75b66b8f68498454d685dc4ba13192ae069b0",
                  "versionType": "git"
                },
                {
                  "lessThan": "a723a6c8d4831cc8e2c7b0c9f3f0c010d4671964",
                  "status": "affected",
                  "version": "9fd75b66b8f68498454d685dc4ba13192ae069b0",
                  "versionType": "git"
                },
                {
                  "lessThan": "3c34fb0bd4a4237592c5ecb5b2e2531900c55774",
                  "status": "affected",
                  "version": "9fd75b66b8f68498454d685dc4ba13192ae069b0",
                  "versionType": "git"
                },
                {
                  "status": "affected",
                  "version": "c44a453ffe16eb08acdc6129ac4fa0192dbc0456",
                  "versionType": "git"
                },
                {
                  "status": "affected",
                  "version": "de55a1338e6a48ff1e41ea8db1432496fbe2a62b",
                  "versionType": "git"
                },
                {
                  "status": "affected",
                  "version": "9e1e088a57c23251f1cfe9601bbd90ade2ea73b9",
                  "versionType": "git"
                },
                {
                  "status": "affected",
                  "version": "b20a5ab0f5fb175750c6bafd4cf12daccf00c738",
                  "versionType": "git"
                },
                {
                  "status": "affected",
                  "version": "452ae92b99062d2f6a34324eaf705a3b7eac9f8b",
                  "versionType": "git"
                },
                {
                  "status": "affected",
                  "version": "534156dd4ed768e30a43de0036f45dca7c54818f",
                  "versionType": "git"
                },
                {
                  "lessThan": "4.15",
                  "status": "affected",
                  "version": "4.14.277",
                  "versionType": "semver"
                },
                {
                  "lessThan": "4.20",
                  "status": "affected",
                  "version": "4.19.240",
                  "versionType": "semver"
                },
                {
                  "lessThan": "5.5",
                  "status": "affected",
                  "version": "5.4.190",
                  "versionType": "semver"
                },
                {
                  "lessThan": "5.11",
                  "status": "affected",
                  "version": "5.10.112",
                  "versionType": "semver"
                },
                {
                  "lessThan": "5.16",
                  "status": "affected",
                  "version": "5.15.35",
                  "versionType": "semver"
                },
                {
                  "lessThan": "5.18",
                  "status": "affected",
                  "version": "5.17.2",
                  "versionType": "semver"
                }
              ]
            },
            {
              "defaultStatus": "affected",
              "product": "Linux",
              "programFiles": [
                "net/ax25/af_ax25.c"
              ],
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "vendor": "Linux",
              "versions": [
                {
                  "status": "affected",
                  "version": "5.18"
                },
                {
                  "lessThan": "5.18",
                  "status": "unaffected",
                  "version": "0",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "6.1.*",
                  "status": "unaffected",
                  "version": "6.1.95",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "6.6.*",
                  "status": "unaffected",
                  "version": "6.6.35",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "6.9.*",
                  "status": "unaffected",
                  "version": "6.9.6",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "*",
                  "status": "unaffected",
                  "version": "6.10",
                  "versionType": "original_commit_for_fix"
                }
              ]
            }
          ],
          "cpeApplicability": [
            {
              "nodes": [
                {
                  "cpeMatch": [
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "6.1.95",
                      "versionStartIncluding": "5.18",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "6.6.35",
                      "versionStartIncluding": "5.18",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "6.9.6",
                      "versionStartIncluding": "5.18",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "6.10",
                      "versionStartIncluding": "5.18",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionStartIncluding": "4.14.277",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionStartIncluding": "4.19.240",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionStartIncluding": "5.4.190",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionStartIncluding": "5.10.112",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionStartIncluding": "5.15.35",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionStartIncluding": "5.17.2",
                      "vulnerable": true
                    }
                  ],
                  "negate": false,
                  "operator": "OR"
                }
              ]
            }
          ],
          "descriptions": [
            {
              "lang": "en",
              "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nax25: Fix refcount imbalance on inbound connections\n\nWhen releasing a socket in ax25_release(), we call netdev_put() to\ndecrease the refcount on the associated ax.25 device. However, the\nexecution path for accepting an incoming connection never calls\nnetdev_hold(). This imbalance leads to refcount errors, and ultimately\nto kernel crashes.\n\nA typical call trace for the above situation will start with one of the\nfollowing errors:\n\n    refcount_t: decrement hit 0; leaking memory.\n    refcount_t: underflow; use-after-free.\n\nAnd will then have a trace like:\n\n    Call Trace:\n    \u003cTASK\u003e\n    ? show_regs+0x64/0x70\n    ? __warn+0x83/0x120\n    ? refcount_warn_saturate+0xb2/0x100\n    ? report_bug+0x158/0x190\n    ? prb_read_valid+0x20/0x30\n    ? handle_bug+0x3e/0x70\n    ? exc_invalid_op+0x1c/0x70\n    ? asm_exc_invalid_op+0x1f/0x30\n    ? refcount_warn_saturate+0xb2/0x100\n    ? refcount_warn_saturate+0xb2/0x100\n    ax25_release+0x2ad/0x360\n    __sock_release+0x35/0xa0\n    sock_close+0x19/0x20\n    [...]\n\nOn reboot (or any attempt to remove the interface), the kernel gets\nstuck in an infinite loop:\n\n    unregister_netdevice: waiting for ax0 to become free. Usage count = 0\n\nThis patch corrects these issues by ensuring that we call netdev_hold()\nand ax25_dev_hold() for new connections in ax25_accept(). This makes the\nlogic leading to ax25_accept() match the logic for ax25_bind(): in both\ncases we increment the refcount, which is ultimately decremented in\nax25_release()."
            }
          ],
          "metrics": [
            {
              "cvssV3_1": {
                "baseScore": 8.8,
                "baseSeverity": "HIGH",
                "vectorString": "CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
                "version": "3.1"
              },
              "scenarios": [
                {
                  "lang": "en",
                  "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."
                }
              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-08-05T11:33:57.773Z",
            "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "shortName": "Linux"
          },
          "references": [
            {
              "url": "https://git.kernel.org/stable/c/f4df9d6c8d4e4c818252b0419c2165d66eabd4eb"
            },
            {
              "url": "https://git.kernel.org/stable/c/52100fd74ad07b53a4666feafff1cd11436362d3"
            },
            {
              "url": "https://git.kernel.org/stable/c/a723a6c8d4831cc8e2c7b0c9f3f0c010d4671964"
            },
            {
              "url": "https://git.kernel.org/stable/c/3c34fb0bd4a4237592c5ecb5b2e2531900c55774"
            }
          ],
          "title": "ax25: Fix refcount imbalance on inbound connections",
          "x_generator": {
            "engine": "bippy-1.2.0"
          }
        }
      },
      "cveMetadata": {
        "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "assignerShortName": "Linux",
        "cveId": "CVE-2024-40910",
        "datePublished": "2024-07-12T12:20:49.085Z",
        "dateReserved": "2024-07-12T12:17:45.580Z",
        "dateUpdated": "2026-08-05T11:33:57.773Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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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.


Detection rules are retrieved from Rulezet.


Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.