{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2024-40910", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2024-07-12T12:17:45.580Z", "datePublished": "2024-07-12T12:20:49.085Z", "dateUpdated": "2026-08-05T11:33:57.773Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T11:33:57.773Z" }, "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 \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": { "version": "3.1", "vectorString": "CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H", "baseScore": 8.8, "baseSeverity": "HIGH" }, "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->refcount` to zero. No race, no memory-layout precondition, and the attacker controls the repetition count.\nPR:N - AX.25 has no authentication whatsoever — 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->ax25_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 — 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 — a permanent, remotely inducible hang in addition to the UAF oops." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/ax25/af_ax25.c" ], "versions": [ { "version": "9fd75b66b8f68498454d685dc4ba13192ae069b0", "lessThan": "f4df9d6c8d4e4c818252b0419c2165d66eabd4eb", "status": "affected", "versionType": "git" }, { "version": "9fd75b66b8f68498454d685dc4ba13192ae069b0", "lessThan": "52100fd74ad07b53a4666feafff1cd11436362d3", "status": "affected", "versionType": "git" }, { "version": "9fd75b66b8f68498454d685dc4ba13192ae069b0", "lessThan": "a723a6c8d4831cc8e2c7b0c9f3f0c010d4671964", "status": "affected", "versionType": "git" }, { "version": "9fd75b66b8f68498454d685dc4ba13192ae069b0", "lessThan": "3c34fb0bd4a4237592c5ecb5b2e2531900c55774", "status": "affected", "versionType": "git" }, { "version": "c44a453ffe16eb08acdc6129ac4fa0192dbc0456", "status": "affected", "versionType": "git" }, { "version": "de55a1338e6a48ff1e41ea8db1432496fbe2a62b", "status": "affected", "versionType": "git" }, { "version": "9e1e088a57c23251f1cfe9601bbd90ade2ea73b9", "status": "affected", "versionType": "git" }, { "version": "b20a5ab0f5fb175750c6bafd4cf12daccf00c738", "status": "affected", "versionType": "git" }, { "version": "452ae92b99062d2f6a34324eaf705a3b7eac9f8b", "status": "affected", "versionType": "git" }, { "version": "534156dd4ed768e30a43de0036f45dca7c54818f", "status": "affected", "versionType": "git" }, { "version": "4.14.277", "lessThan": "4.15", "status": "affected", "versionType": "semver" }, { "version": "4.19.240", "lessThan": "4.20", "status": "affected", "versionType": "semver" }, { "version": "5.4.190", "lessThan": "5.5", "status": "affected", "versionType": "semver" }, { "version": "5.10.112", "lessThan": "5.11", "status": "affected", "versionType": "semver" }, { "version": "5.15.35", "lessThan": "5.16", "status": "affected", "versionType": "semver" }, { "version": "5.17.2", "lessThan": "5.18", "status": "affected", "versionType": "semver" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/ax25/af_ax25.c" ], "versions": [ { "version": "5.18", "status": "affected" }, { "version": "0", "lessThan": "5.18", "status": "unaffected", "versionType": "semver" }, { "version": "6.1.95", "lessThanOrEqual": "6.1.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.6.35", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.9.6", "lessThanOrEqual": "6.9.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.10", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.18", "versionEndExcluding": "6.1.95" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.18", "versionEndExcluding": "6.6.35" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.18", "versionEndExcluding": "6.9.6" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.18", "versionEndExcluding": "6.10" }, { "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": 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