GHSA-C6XM-FH9C-399H
Vulnerability from github – Published: 2026-08-22 18:30 – Updated: 2026-08-25 06:31In the Linux kernel, the following vulnerability has been resolved:
tipc: read le->link under the node lock in tipc_node_link_down()
tipc_node_link_down() caches the link pointer before taking n->lock:
struct tipc_link *l = le->link; /* unlocked */
if (!l)
return;
tipc_node_write_lock(n);
if (!tipc_link_is_establishing(l)) { /* deref l */
...
tipc_link_reset(l); /* write into l */
if (delete) {
kfree(l);
le->link = NULL;
The delete=true caller frees that very object under n->lock, so the lock does not protect the cached pointer against it:
- CPU A, delete=false: tipc_rcv() on TIPC_LINK_DOWN_EVT, or the link supervision timer via tipc_node_timeout(), reads l unlocked and then dereferences it under n->lock;
- CPU B, delete=true: netlink TIPC_NL_BEARER_DISABLE -> bearer_disable() -> tipc_node_delete_links() -> tipc_node_link_down(n, bearer_id, true) -> kfree(l).
The link is freed with plain kfree(), not kfree_rcu(), and for UDP bearers disable_media() only schedules the asynchronous cleanup_bearer() work, so its synchronize_net() runs after the links are already gone. An in-flight CPU A that has read l therefore dereferences freed memory once B frees it: a use-after-free read in tipc_link_is_establishing(), and a use-after-free write via tipc_link_reset() on the establishing branch.
The following trace was captured on 7.2.0-rc5-00284-gaf39eb111ce6:
BUG: KASAN: slab-use-after-free in tipc_link_is_establishing (net/tipc/link.c:285) Read of size 4 at addr ffff88802e2aa068 by task swapper/2/0 tipc_link_is_establishing (net/tipc/link.c:285) tipc_node_link_down (net/tipc/node.c:1076) tipc_node_timeout (net/tipc/node.c:843) Allocated by task 9549: tipc_link_create (net/tipc/link.c:490) tipc_node_check_dest (net/tipc/node.c:1279) tipc_disc_rcv (net/tipc/discover.c:252) tipc_udp_recv (net/tipc/udp_media.c:389) Freed by task 9549: tipc_node_link_down (net/tipc/node.c:1084) tipc_node_delete_links (net/tipc/node.c:1320) bearer_disable (net/tipc/bearer.c:414) __tipc_nl_bearer_disable (net/tipc/bearer.c:992)
Move the le->link read inside tipc_node_write_lock(), so it is serialised against the kfree() in the delete path. A racing teardown now either has not run yet, and we see a valid link, or has already run, and we see NULL.
{
"affected": [],
"aliases": [
"CVE-2026-74609"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-08-22T16:16:33Z",
"severity": "HIGH"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\ntipc: read le-\u003elink under the node lock in tipc_node_link_down()\n\ntipc_node_link_down() caches the link pointer before taking n-\u003elock:\n\n\tstruct tipc_link *l = le-\u003elink;\t\t/* unlocked */\n\n\tif (!l)\n\t\treturn;\n\ttipc_node_write_lock(n);\n\tif (!tipc_link_is_establishing(l)) {\t/* deref l */\n\t...\n\t\ttipc_link_reset(l);\t\t/* write into l */\n\tif (delete) {\n\t\tkfree(l);\n\t\tle-\u003elink = NULL;\n\nThe delete=true caller frees that very object under n-\u003elock, so the lock\ndoes not protect the cached pointer against it:\n\n - CPU A, delete=false: tipc_rcv() on TIPC_LINK_DOWN_EVT, or the link\n supervision timer via tipc_node_timeout(), reads l unlocked and then\n dereferences it under n-\u003elock;\n - CPU B, delete=true: netlink TIPC_NL_BEARER_DISABLE -\u003e bearer_disable()\n -\u003e tipc_node_delete_links() -\u003e tipc_node_link_down(n, bearer_id, true)\n -\u003e kfree(l).\n\nThe link is freed with plain kfree(), not kfree_rcu(), and for UDP bearers\ndisable_media() only schedules the asynchronous cleanup_bearer() work, so\nits synchronize_net() runs after the links are already gone. An in-flight\nCPU A that has read l therefore dereferences freed memory once B frees it:\na use-after-free read in tipc_link_is_establishing(), and a use-after-free\nwrite via tipc_link_reset() on the establishing branch.\n\nThe following trace was captured on 7.2.0-rc5-00284-gaf39eb111ce6:\n\n BUG: KASAN: slab-use-after-free in tipc_link_is_establishing (net/tipc/link.c:285)\n Read of size 4 at addr ffff88802e2aa068 by task swapper/2/0\n tipc_link_is_establishing (net/tipc/link.c:285)\n tipc_node_link_down (net/tipc/node.c:1076)\n tipc_node_timeout (net/tipc/node.c:843)\n Allocated by task 9549:\n tipc_link_create (net/tipc/link.c:490)\n tipc_node_check_dest (net/tipc/node.c:1279)\n tipc_disc_rcv (net/tipc/discover.c:252)\n tipc_udp_recv (net/tipc/udp_media.c:389)\n Freed by task 9549:\n tipc_node_link_down (net/tipc/node.c:1084)\n tipc_node_delete_links (net/tipc/node.c:1320)\n bearer_disable (net/tipc/bearer.c:414)\n __tipc_nl_bearer_disable (net/tipc/bearer.c:992)\n\nMove the le-\u003elink read inside tipc_node_write_lock(), so it is serialised\nagainst the kfree() in the delete path. A racing teardown now either has\nnot run yet, and we see a valid link, or has already run, and we see NULL.",
"id": "GHSA-c6xm-fh9c-399h",
"modified": "2026-08-25T06:31:22Z",
"published": "2026-08-22T18:30:26Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-74609"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/2be741ad565c610871a6a95062c12c39da7168fd"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/47ba70891b10b2feb52462086b7fcd2ad75d3ce3"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/5558a8312452ddb21eff22b1cbd84302ad951944"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/69d209461c110388710e483a130caf051e4fd09a"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/a714d62513befef37f71f4ae89bb1fe173b65f2e"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/c3f2347a47754eac690967cfd82cb6d559817b07"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/cba9ccb47e9fa4cc77692fb896cc5ab57a667882"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/de017c22135f545ca4e65d1eada22887b64958eb"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
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- Confirmed: The vulnerability has been validated from an analyst's perspective.
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- 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 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.