CVE-2026-68398 (GCVE-0-2026-68398)
Vulnerability from cvelistv5
Published
2026-08-10 12:04
Modified
2026-08-19 16:34
Severity ?
VLAI Severity ?
EPSS score ?
Summary
In the Linux kernel, the following vulnerability has been resolved:
ppp: defer channel free to an RCU grace period to fix pppol2tp RX UAF
pppol2tp_recv() runs in the L2TP UDP-encap softirq RX path:
l2tp_udp_encap_recv() -> l2tp_recv_common() -> pppol2tp_recv()
-> ppp_input(&po->chan)
It runs under rcu_read_lock() holding only an l2tp_session reference and
takes NO reference on the internal PPP channel (struct channel,
chan->ppp) that ppp_input() dereferences.
The pppox socket is SOCK_RCU_FREE, so 'po' and the embedded ppp_channel
are RCU-safe. But the internal struct channel is a separate allocation
that ppp_release_channel() frees with a plain kfree():
close(data socket) -> pppol2tp_release() -> pppox_unbind_sock()
-> ppp_unregister_channel() -> ppp_release_channel() -> kfree(pch)
For a channel that is bound (PPPIOCGCHAN) but not attached to a ppp unit
(no PPPIOCCONNECT, pch->ppp == NULL) and not bridged, teardown skips
both ppp_disconnect_channel()'s synchronize_net() and
ppp_unbridge_channels()'s synchronize_rcu(), so the kfree() has no grace
period. rcu_read_lock() in pppol2tp_recv() does not protect against a
plain kfree(), so an in-flight ppp_input() on one CPU can dereference
the channel just freed by close() on another CPU.
The bug is reachable by an unprivileged user.
Defer the channel free to an RCU callback via call_rcu() so the grace
period fences any in-flight ppp_input(). The disconnect and unbridge
teardown paths already fence with synchronize_net()/synchronize_rcu();
call_rcu() does the same here without stalling the close() path.
References
Impacted products
| Vendor | Product | Version | ||
|---|---|---|---|---|
| Linux | Linux |
Version: ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 Version: ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 Version: ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 Version: ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 Version: ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 Version: ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 Version: ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 Version: d36e5ba7bbed5d7bd26e8609ffed503c2def401b Version: 9bcc0508576b2d50efd958f2ea1c5906749c2c89 Version: c2984681fe15cfb803a9132aaaf1140ab20a72c1 Version: 5803ecd7f6ac6f747582e775caa62ac9d0489261 Version: 26f8819ddd10141ebe7bbce700fbab36bfa5f478 Version: 3.2.99 ≤ Version: 3.16.54 ≤ Version: 4.4.225 ≤ Version: 4.9.225 ≤ Version: 4.14.182 ≤ |
||
{
"containers": {
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{
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"product": "Linux",
"programFiles": [
"drivers/net/ppp/ppp_generic.c"
],
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"vendor": "Linux",
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},
{
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{
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{
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{
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{
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{
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{
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"versionType": "git"
},
{
"lessThan": "3.3",
"status": "affected",
"version": "3.2.99",
"versionType": "semver"
},
{
"lessThan": "3.17",
"status": "affected",
"version": "3.16.54",
"versionType": "semver"
},
{
"lessThan": "4.5",
"status": "affected",
"version": "4.4.225",
"versionType": "semver"
},
{
"lessThan": "4.10",
"status": "affected",
"version": "4.9.225",
"versionType": "semver"
},
{
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"status": "affected",
"version": "4.14.182",
"versionType": "semver"
}
]
},
{
"defaultStatus": "affected",
"product": "Linux",
"programFiles": [
"drivers/net/ppp/ppp_generic.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"status": "affected",
"version": "4.15"
},
{
"lessThan": "4.15",
"status": "unaffected",
"version": "0",
"versionType": "semver"
},
{
"lessThanOrEqual": "5.15.*",
"status": "unaffected",
"version": "5.15.216",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.1.*",
"status": "unaffected",
"version": "6.1.183",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.6.*",
"status": "unaffected",
"version": "6.6.148",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.12.*",
"status": "unaffected",
"version": "6.12.101",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.18.*",
"status": "unaffected",
"version": "6.18.42",
"versionType": "semver"
},
{
"lessThanOrEqual": "7.1.*",
"status": "unaffected",
"version": "7.1.6",
"versionType": "semver"
},
{
"lessThanOrEqual": "*",
"status": "unaffected",
"version": "7.2",
"versionType": "original_commit_for_fix"
}
]
}
],
"cpeApplicability": [
{
"nodes": [
{
"cpeMatch": [
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "5.15.216",
"versionStartIncluding": "4.15",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "6.1.183",
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},
{
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"vulnerable": true
},
{
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"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "6.18.42",
"versionStartIncluding": "4.15",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "7.1.6",
"versionStartIncluding": "4.15",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "7.2",
"versionStartIncluding": "4.15",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionStartIncluding": "3.2.99",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionStartIncluding": "3.16.54",
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},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionStartIncluding": "4.4.225",
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},
{
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},
{
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"versionStartIncluding": "4.14.182",
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}
],
"negate": false,
"operator": "OR"
}
]
}
],
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nppp: defer channel free to an RCU grace period to fix pppol2tp RX UAF\n\npppol2tp_recv() runs in the L2TP UDP-encap softirq RX path:\n\n l2tp_udp_encap_recv() -\u003e l2tp_recv_common() -\u003e pppol2tp_recv()\n -\u003e ppp_input(\u0026po-\u003echan)\n\nIt runs under rcu_read_lock() holding only an l2tp_session reference and\ntakes NO reference on the internal PPP channel (struct channel,\nchan-\u003eppp) that ppp_input() dereferences.\n\nThe pppox socket is SOCK_RCU_FREE, so \u0027po\u0027 and the embedded ppp_channel\nare RCU-safe. But the internal struct channel is a separate allocation\nthat ppp_release_channel() frees with a plain kfree():\n\n close(data socket) -\u003e pppol2tp_release() -\u003e pppox_unbind_sock()\n -\u003e ppp_unregister_channel() -\u003e ppp_release_channel() -\u003e kfree(pch)\n\nFor a channel that is bound (PPPIOCGCHAN) but not attached to a ppp unit\n(no PPPIOCCONNECT, pch-\u003eppp == NULL) and not bridged, teardown skips\nboth ppp_disconnect_channel()\u0027s synchronize_net() and\nppp_unbridge_channels()\u0027s synchronize_rcu(), so the kfree() has no grace\nperiod. rcu_read_lock() in pppol2tp_recv() does not protect against a\nplain kfree(), so an in-flight ppp_input() on one CPU can dereference\nthe channel just freed by close() on another CPU.\n\nThe bug is reachable by an unprivileged user.\n\nDefer the channel free to an RCU callback via call_rcu() so the grace\nperiod fences any in-flight ppp_input(). The disconnect and unbridge\nteardown paths already fence with synchronize_net()/synchronize_rcu();\ncall_rcu() does the same here without stalling the close() path."
}
],
"metrics": [
{
"cvssV3_1": {
"baseScore": 7.8,
"baseSeverity": "HIGH",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
"scenarios": [
{
"lang": "en",
"value": "AV:L - The free side of the race is a local close() of the pppol2tp socket, which no remote peer can invoke; the full attack (create tunnel/session via AF_PPPOX socket, drive RX with loopback UDP datagrams, close concurrently) is performed entirely through local syscalls.\nAC:L - The attacker controls both sides of the race, feeding the UDP-encap RX softirq from one thread while closing the pppox socket on another, and can retry the loop indefinitely until the window is hit.\nPR:L - No capability check exists on this path: pppox_create()/pppol2tp_connect() and ppp_register_net_channel() need no CAP_NET_ADMIN, and PPPIOCGCHAN is handled by pppox_ioctl() on the socket itself, so /dev/ppp access is not required; the fix commit states the bug is reachable by an unprivileged user.\nUI:N - The attacker performs every step \u2014 socket creation, session setup, packet injection and close() \u2014 with no action by any other user or administrator.\nS:U - The use-after-free corrupts kernel slab memory within the same kernel security authority; no VM, IOMMU or sandbox boundary is crossed.\nC:H - After the channel is freed and its slab object reallocated, ppp_input() reads pch-\u003ebridge and pch-\u003eppp from attacker-groomed memory and can route received frames to an arbitrary attacker-chosen structure, giving a path to disclosing kernel memory.\nI:H - skb_queue_tail(\u0026pch-\u003efile.rq, skb) writes a linked-list insertion into the freed object and wake_up_interruptible(\u0026pch-\u003efile.rwait) traverses a freed waitqueue, so heap grooming yields controlled writes and function-pointer traversal usable for privilege escalation.\nA:H - Dereferencing and writing to the kfree()d struct channel from softirq context reliably corrupts the slab and panics or oopses the kernel, and the race can be re-triggered at will."
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-08-19T16:34:49.839Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
},
"references": [
{
"url": "https://git.kernel.org/stable/c/4e47f1ac188ece11d6fdabe44166a2776cc5bd4e"
},
{
"url": "https://git.kernel.org/stable/c/110b765744b147c63882f5e9cb12931c5dc8d85f"
},
{
"url": "https://git.kernel.org/stable/c/4bb84e964ff0fe0a171c965362de72f9820dbce9"
},
{
"url": "https://git.kernel.org/stable/c/3ab32218d7182705dae5c86f13925f458072da2c"
},
{
"url": "https://git.kernel.org/stable/c/c9574b8a8edeb4edd3ac6472c27ef7184bdb2baa"
},
{
"url": "https://git.kernel.org/stable/c/06213c85d8c0994f786c093b8b2a517987943ca6"
},
{
"url": "https://git.kernel.org/stable/c/ec4215683e47424c9c4762fd3c60f552a3119142"
}
],
"title": "ppp: defer channel free to an RCU grace period to fix pppol2tp RX UAF",
"x_generator": {
"engine": "bippy-1.2.0"
}
}
},
"cveMetadata": {
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"assignerShortName": "Linux",
"cveId": "CVE-2026-68398",
"datePublished": "2026-08-10T12:04:17.771Z",
"dateReserved": "2026-07-30T09:28:09.389Z",
"dateUpdated": "2026-08-19T16:34:49.839Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.
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