GHSA-FP3M-QH7P-HCJ7
Vulnerability from github – Published: 2026-08-22 18:30 – Updated: 2026-08-27 15:31In the Linux kernel, the following vulnerability has been resolved:
net/x25: fix use-after-free of the socket by its timers
The x25 timers are armed with mod_timer() and cancelled with timer_delete(), so a pending timer holds no reference on the socket and a cancel does not wait for a callback already running on another CPU.
x25_heartbeat_expiry() also rearms unconditionally, so it can reinstall sk->sk_timer after __x25_destroy_socket() has passed its cancel point. The following __sock_put() frees the socket while the timer is still queued, and the next expiry uses freed memory. KASAN reports a slab-use-after-free on the kmalloc-2k object freed by close().
timer_delete_sync() cannot be used here: x25_heartbeat_expiry() and x25_timer_expiry() both reach the cancels from inside the timer they would wait on, through __x25_destroy_socket() and x25_disconnect().
Arm the timers with sk_reset_timer() and cancel them with sk_stop_timer() so that an armed timer owns a reference, and release it in both expiry handlers. Rearm the heartbeat only while sk_hashed(sk) is still true, since __x25_destroy_socket() unlinks the socket before dropping it. Arm the deferred destroy timer the same way and drop its reference in x25_destroy_timer().
Reproduced on net with KASAN, with the heartbeat period shortened so the window recurs. With this patch the reproducer no longer triggers a report and /proc/net/x25 drains.
Discovered by XBOW, triaged by Baul Lee baul.lee@xbow.com
{
"affected": [],
"aliases": [
"CVE-2026-74628"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-08-22T16:16:35Z",
"severity": "CRITICAL"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/x25: fix use-after-free of the socket by its timers\n\nThe x25 timers are armed with mod_timer() and cancelled with\ntimer_delete(), so a pending timer holds no reference on the socket and a\ncancel does not wait for a callback already running on another CPU.\n\nx25_heartbeat_expiry() also rearms unconditionally, so it can reinstall\nsk-\u003esk_timer after __x25_destroy_socket() has passed its cancel point.\nThe following __sock_put() frees the socket while the timer is still\nqueued, and the next expiry uses freed memory. KASAN reports a\nslab-use-after-free on the kmalloc-2k object freed by close().\n\ntimer_delete_sync() cannot be used here: x25_heartbeat_expiry() and\nx25_timer_expiry() both reach the cancels from inside the timer they\nwould wait on, through __x25_destroy_socket() and x25_disconnect().\n\nArm the timers with sk_reset_timer() and cancel them with sk_stop_timer()\nso that an armed timer owns a reference, and release it in both expiry\nhandlers. Rearm the heartbeat only while sk_hashed(sk) is still true,\nsince __x25_destroy_socket() unlinks the socket before dropping it. Arm\nthe deferred destroy timer the same way and drop its reference in\nx25_destroy_timer().\n\nReproduced on net with KASAN, with the heartbeat period shortened so the\nwindow recurs. With this patch the reproducer no longer triggers a\nreport and /proc/net/x25 drains.\n\nDiscovered by XBOW, triaged by Baul Lee \u003cbaul.lee@xbow.com\u003e",
"id": "GHSA-fp3m-qh7p-hcj7",
"modified": "2026-08-27T15:31:29Z",
"published": "2026-08-22T18:30:27Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-74628"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/1fc9f6d2c7c9fdb341bfe8ca449c990632299ea6"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/2195424c3da2ef1829a63b807e3a900a90e57d85"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/3c4919be5d910db4beebca420953858606fba7d8"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/4bc522b33438fefc3272840ae5988771863a4f1f"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/6b79659590f0f82a9b8efd2ffd55ec6399ebfc33"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/ba925a2e98ce967a0e71c5bcbcf5dbd3facaf0c8"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/e92c7e2b41d1528a830bc64c5e4e46dfa8133dda"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/fdd9ac50b9b61ef2b2d52c5156aff788be91454d"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
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